J. Chem. Soc. Perkin Trans. 1 1997 747 First examples of arylazo derivatives of cyclooctatetraene † Zori V. Todres and Ghevork Ts. Hovsepyan Research Institute The Cleveland Clinic Foundation 4075 Monticello Boulevard #205A Cleveland Ohio 44121 USA Disodium and dipotassium derivatives of 1,6-dinitrocyclooctatetraene (substrates) react with benzenediazo compounds (reagents) in THF to yield bis(azo)- or nitro(azo)-cyclooctatetraenes the first cyclooctatetraene arylazo derivatives. Structures of the azo compounds are established by conventional methods and confirmed by X-ray crystallography. Together with the main products of electrophilic substitution products of substrate-to-reagent electron transfer are formed. The electron-transfer products predominate with DMSO instead of THF as a solvent.The difference is apparently a result of ion-pair disintegration in the case of the substrate reactions when DMSO a strong dissociating solvent is used. Introduction The present work describes the study of alkali metal compounds of nitro and azoxy derivatives which exhibit distinct organometallic character and differ fundamentally in reactivity from their respective anion-radicals and dianions which have separate alkali-metal counterions.2,3 Here we focus on the disodium and dipotassium derivatives of 1,6-dinitrocycloocta- 1,3,5,7-tetraene 1. The neutral molecule of 1 has a boat conformation with the two nitro groups located above the boat.4 For the di(Na/K) derivative of 1 planar and non-planar structures are theoretically possible. The planar form 2 is characterized by delocalization of the two excess electrons in the eight-membered ring.The same manner of delocalization is characteristic for the di(Na/K) derivative of unsubstituted cyclooctatetraene (COT) and dimethyl-COT.5 The non-planar form 3 requires fixation of the two excess electrons at the two nitro groups blocked by two alkali metals (see Scheme 1). Conditions for existence of forms 2 and 3 The di(Na/K) derivatives of 1 were prepared by means of interchange between 1 and di(Na/K) derivatives of COT in tetrahydrofuran (THF). An alternative approach consisted of treatment of 1,4-dinitrocycloocta-2,5,7-triene with (Na/K) methoxides in methanol. By means of spectral [IR NMR (1H 13C)] methods we earlier found that form 3 became stable in non-dissociating solvents.6 In other words the salts of the dianion of 1 exist in the form of ion pairs and the excess negative charges are localized primarily on the nitro groups.In dissociating solvents the ion pairs are broken up and free ions are formed. This leads to a considerable shift of electron density in the eight-membered ring see structure 2.6 We had concluded in our earlier work6 that the difference between forms 2 and 3 must be reflected in their reactivity. The increase in delocalization of the excess electrons which is a consequence of dissociation of the ion pairs must lead to an increase in the level of the donor properties of the substrates. Thus when the free dianion 2 is treated with electrophiles it will more readily give up electrons than it will enter into electrophilic substitution. The characteristic reaction of electrophilic substitution of an aci-nitro group (NOO2M+) in contrast should proceed more readily in non-dissociating solvents when the substrates act as the ion pairs 3.6 † This work was initially presented in the VI International Conference on Organic Synthesis.1 The aim of our present study was to verify the prediction for the case of azo coupling and if successful to obtain new arylazo derivatives of cyclooctatetraene.Interaction between di(Na/K) derivatives of 1 and benzenediazo cations In THF or 1,2-dimethoxyethane (DME) the disodium or dipotassium derivative of 1 reacts with benzenediazo cations in two ways. One of them the minor is one-electron reduction of the cations. It results in N2 evolution and formation of 1 and benzene derivatives RC6H5 (see Scheme 2 and Table 1). This reaction proceeds to 10–20% only whereas the main route is the formation of bis(azo) and nitro(azo) derivatives of COT.All appearances suggest that the key stage of the reaction is ipso-coupling with intermediates 4 and 5 probably being formed (see Scheme 3). Alkali nitrite is cleaved from the intermediate 4 while dinitrogen tetroxide is liberated from the intermediate 5. At the same time the cyclooctatriene ring is transformed into a cyclooctatetraene ring to give the final products 6 and 7. Transformation of 5 into 6 is also possible (with elimination of p-RC6H4N2NO2). Mono 6a–c and bis(azo) derivatives 7a–c are obtained together irrespective of the stoichiometric relationship between the reagents and the substrate. Under similar conditions yields Scheme 1 NO2 O2N O2N NO2 = M+ M+ MOON NOOM +2e +2M+ +2e +2M+ 2 1 3 M = Na K 748 J.Chem. Soc. Perkin Trans. 1 1997 of nitroazo compounds 6 increase and yields of bis(azo) compounds 7 decrease along with a decrease in the acceptor ability of the substituent R in the benzenediazo cation. Where R ]] NMe2 only monosubstitution takes place with formation of product 6d. All the above mentioned data are collected in Table 1. The coupling activity of aryldiazo cations drops with a change of R from acceptor to donor. The 1-nitro-6-benzeneazo derivatives 6a–d and 1,6-bis- (benzeneazo) derivatives 7a–c formed are crystals with bright colours from yellow to brown. They are air-stable soluble in organic solvents (acetone benzene chloroform) and have sharp mps (see Tables 2 and 3). Elemental analytical results are compatible with the structural formulae of 6 and 7.The mass spectra of all the compounds prepared show molecular ion peaks (M~+) with intensities in the range 0.4–5% of the total ion current. The major fragmentation pathways for the M~+ are related to cleavage of the bonds between the nitrogen and carbon atoms of the Scheme 2 2 + 2 ( p -RC6H4N2BF4) –2 (MBF4) O2N NO2 + 2 [ p -RC6H4N2 • ] ; 1 [ p -RC6H4N2 • ] [ p -RC6H4 • ] RC6H5 +H• –N2 M = Na K; R = NO2 SCN OMe NMe2 Scheme 3 MOON O2N O2N N2Ar N2Ar ArN2 O2N –MNO2 N2Ar 4 NO2 6 Ar = p-RC6H4 ArN2 N2Ar M = Na K; R = a NO2; b SCN; c OMe; d NMe2 7 5 –N2O4 Ar = p-RC6H4 R = a NO2; b SCN; c OMe; Table 1 Interaction between disodium 1,6-dinitrocyclooctatetraene and tetrafluoroborates of diazo cations with general formula p- RC6H4N2BF4 (substrate reagent ratio 1 2; reaction temperature is 25 8C) Yield (%) Reagent (R) Solvent N2 RPh 1 6 7 NMe2 OMe SCN NO2 THF DMSO THF THF THF DMSO 8 42 12 18 22 71 6 21 4 15 18 53 4 36 5 14 14 52 88 27 57 38 30 6 00 26 34 39 4 COT rings; this corresponds to elimination of (M-NO2)+ and (M-RC6H4N2)+ fragments.Peaks of the (RC6H4)+ ion are the most intense in each case.7 Our preliminary work7 gives a full interpretation of the mass spectra of compounds 6 and 7. From the 1H NMR spectra of compounds 6 and 7 it was possible to identify the AA9 BB9 signals of the phenyl protons with their characteristic 9 Hz coupling; similarly signals from the proton-containing benzene substituents were also identifi- able (see Table 2). The eight-membered ring protons however showed broad signals in the region of d 6–8.The line widening resulted from very fast interchange between the 1,6- and 1,4- valence isomers at ambient temperature (25 8C). To complete the structural proof an X-ray analysis was performed for 1-nitro-6-(4-thiocyanatobenzeneazo)cycloocta- 1,3,5,7-tetraene as a typical example. Published separately,4 the structure is depicted in Fig. 1. The formation of the products in Scheme 3 have also been demonstrated. Sodium or potassium nitrite was shown to be present by IR spectroscopy in the residue from the reaction. The presence of dinitrogen tetroxide in the reaction mixture leads to formation of tarry products as minor components. The formation of N2O4 was revealed by the radical nitration of a minor electron-transfer product when disodium 1,6-dinitrocyclooctatetraene reacted with p-methoxybenzenediazonium tetrafluoroborate (in air THF as a solvent) to give a new nitro compound (see Scheme 4).Product 8 was isolated in 6% yield and its structure was established by X-ray analysis.8 p-Methoxyphenyl radicals (produced by electron transfer to the diazo cation from the disodium derivative of 1) are likely to form p-methoxyphenol after aerial oxidation. This then scavenges dinitrogen tetroxide to give 4-methoxy-2-nitrophenol 8. ortho-Nitration with respect to the hydroxy group rather than the methoxy group is preferred because of stabilization of the final product 8 by intramolecular hydrogen bonding between the NO2 and OH. If the reaction is conducted under argon nitro-product formation is suppressed. It is unnecessary to conduct the reaction between the dialkali compound 1 and a diazo salt under an argon atmosphere.Moreover without an argon flow it is possible to collect and estimate the volume of nitrogen evolved. The reaction was considered to be complete when the evolution of nitrogen gas had ceased. As seen from Table 1 the maximum yield of nitrogen (22%) is observed for the substrate p-NO2C6H4N2BF4 whilst the minimum (8%) occurs for the substrate p-Me2NC6H4N2BF4. Substrates with para substituents OMe and SCN occupy a middle position (12 and 18%). All comparisons are referred to with THF as the solvent. With DMSO instead of THF there is a sharp increase in nitrogen elimination along with yields of RC6H5. At the same Fig. 1 J. Chem. Soc. Perkin Trans. 1 1997 749 Table 2 Cyclooctatetraene azo compounds obtained according to Table 1 Mp/8C Empirical Azo compound R [solvent] Found (%) formula Calc.(%) dH/ppm 6a 6b 6c 6d 7a 7b 7c NO2 SCN OMe NMe2 NO2 SCN OMe 170 [benzene] 131.5 [benzene] 122.5 [diethyl ether] 152.5 [ethyl acetate] 186 [benzene] 201 [acetone] 178 with decomp. [benzene] C 56.17 H 3.41 N 18.80 C 58.00 H 3.00 N 17.98 S 10.26 C 63.54 H 4.40 N 14.80 C 64.72 H 5.22 N 18.89 C 59.69 H 3.41 N 20.88 C 61.86 H 3.10 N 19.69 C 70.90 H 5.26 N 15.89 C14H10N4O4 C15H10N4O2S C15H13N3O3 C16H16N4O2 C20H14N6O4 C22H14N6S2 C22H20N4O2 C 56.37 H 3.53 N 18.79 C 58.06 H 3.23 N 18.06 S 10.32 C 63.60 H 4.59 N 14.84 C 64.86 H 5.41 N 18.92 C 59.70 H 3.48 N 20.90 C 61.97 H 3.29 N 19.72 C 70.97 H 5.38 N 15.05 8.44 (AA9 2H) 8.00 (BB9 2H) 7.94 (AA9 2H) 7.80 (BB9 2H) 7.83 (BB9 2H) 7.08 (AA9 2H) 3.93 (OMe s 3H) 7.56 (BB9 2H) 6.80 (AA9 2H) 3.10 (NMe2 s 6H) 8.42 (AA9 4H) 8.00 (BB9 4H) 7.92 (AA9 4H) 7.80 (BB9 4H) 7.82 (BB9 4H) 7.08 (AA9 4H) 3.93 (OMe × 2 s 6H) time substitution is suppressed.There is a significant difference in the dissociating power of these two solvents (relative permittivities at 293 K are equal to 7.4 and 49 respectively). Experimental Preparation of dipotassium (disodium) 1,6-dinitro-COT Method 1. A filtered solution of freshly prepared dipotassium COT [from COT (1.04 g) and K (0.95 g)] in THF (40 ml) was added to a solution of 1,6-dinitro-COT (1.94 g 0.01 mol)9 in THF (20 ml) at 240 8C under argon. The reaction mixture was stirred at 240 8C for 30 min after which the temperature was raised to 25 8C. A yellow precipitate of 3 was formed and this was filtered off washed twice with cold THF and dried in vacuo over phosphorus pentoxide to yield a dry solid (2.6 g) (Found C 35.30; H 2.24; N 10.22; K 28.05.Calc. for C8H6K2N2O4 C 35.12; H 2.32; N 10.14; K 27.71%). The disodium derivative of 1,6-dinitro-COT was obtained in the same manner from disodium COT (Found C 40.22; H 2.31; N 11.53; Na 18.92. Calc. for C8H6N2Na2O4 C 40.00; H 2.50; N 11.67; Na 19.17%). Method 2. A solution of 1,4-dinitrocycloocta-2,5,7-triene 10 (1.96 g 0.01 mol) in THF (40 ml) was stirred with dry potassium methoxide (1.41 g 0.02 mol) at 220 8C for 20 min and then warmed to 25 8C over 30 min. Dipotassium 1,6- dinitro-COT was formed as a bright yellow precipitate which was treated as described above. The dry solid was obtained in 94% yield (2.55 g). The disodium analogue was prepared with sodium methoxide.The elemental composition and spectra of the (Na/K) derivatives obtained by methods 1 and 2 were identical. In method 2 1,4-dinitrocyclooctatriene used as a starting Table 3 Absorption bands in the electronic spectra of cyclooctatetraene azo compounds obtained according to Table 1 Azo compound R lmax/nm e × 104/l mol21 cm21 6a 6b 6c 6d 7a 7b 7c NO2 SCN OMe NMe2 NO2 SCN OMe 306 356 236 323 248 342 257 460 304 364 236 322 398 250 342 400 2.20 1.42 0.88 1.06 1.74 1.95 1.46 2.10 3.60 2.04 1.76 2.22 1.25 2.22 3.06 2.76 material was synthesized by nitration of COT with N2O4. The resultant compound was purified by procedures given in ref. 10 to give white crystals which were dried in vacuo (no more than 1 h). Interaction between the dipotassium or disodium derivative of 1,6- dinitro-COT and benzenediazonium tetrafluoroborates a typical procedure A dry tetrafluoroborate (0.01 mol) was slowly added to a suspension of the dipotassium derivative 3 (1.36 g) or disodium derivative 3 (1.20 g 0.05 mol) in THF or DME (40 ml).When DMSO was used as a solvent 10 ml were utilized to dissolve substrate 3 and 20 ml to dissolve the diazo salt. The reaction mixture was stirred over 30 min at 25 8C. Nitrogen was evolved in the course of the reaction and when this ceased the reaction Scheme 4 N2 + MeO N2 • MeO MeO OO• MeO OOH MeO + e OH MeO –N2 • +O2 +H• OH MeO +N2O4 –1/2 O2 NO2 –HNO2 8 750 J. Chem. Soc. Perkin Trans. 1 1997 mixture was stirred for a further 30 min and then filtered; a small quantity of this filtrate was examined by GLC (see below). The remaining filtrate was concentrated to 25% of its original volume.The resulting precipitate was collected and in solution subjected to chromatography (22 × 600 mm silica gel column; eluent hexane–ethyl acetate 3 1). The solid resulting from filtration of the reaction mixture was treated with cold acetone (3 × 10 ml) dried and analysed by means of IR spectroscopy and qualitative analytical methods. The salts MNO2 and MBF4 (M ]] Na K) were shown to be components of the solid although their yields were not determined. The yields of 1,6-dinitro-COT 1 its azo derivatives 6 and 7 nitrogen gas and benzenes RC6H5 are given in Table 1. Tables 2 and 3 show the analytical data upon which identification of the azo products 6 and 7 was established. Quantities of RC6H5 were determined by a GLC method with authentic standard materials introduced into the mixtures being analysed.Nitrogen was used as a carrier gas in all cases. For anisole and N,N-dimethylaniline a stainless-steel column (3 × 3700 mm) was used. The stationary phase was PEG-20M on silanized Chromatone N-AW 40–60 mesh. For phenyl thiocyanate and nitrobenzene a glass column (2 × 2000 mm) was employed. In this case the stationary phase was 5% SE-30 on silanized Chromatone N-AW-DMCS 20–25 mesh. 1H NMR Spectra were obtained on a Bruker WP-200 instrument using (CD3)2CO as a solvent with SiMe4 as a standard. Electronic absorption spectra were recorded using a Specord UV–VIS spectrometer and a cuvette of 1 cm diameter with MeOH as solvent and with 1023 mol l21 concentrations of the azo compounds. References 1 Z. V. Todres G.Ts. Hovsepyan in Abstracts of papers of the VI International Conference on Organic Synthesis August 10–15 1986 Moscow Russia. 2 Z. V. Todres J. Organomet. Chem. 1992 441 349. 3 Z. V. Todres S. P. Avagyan and D. N. Kursanov J. Organomet. Chem. 1975 97 139. 4 Z. V. Todres G. Ts. Hovsepyan V. I. Bakhmutov A. Yu. Kosnikov S. V. Lindeman and Yu. T. Struchkov Zh. Org. Khim. 1989 25 75 (in Russian) (Chem. Abstr. 1989 111 77532t). 5 G. J. Fray and R. G. Saxton The Chemistry of Cyclo-octatetraene and Its Derivatives Cambridge University Press London 1978 p. 48. 6 Z. V. Todres G. Ts. Hovsepyan I. A. Garbuzova I. V. Stankevich and V. I. Bakhmutov Izv. Akad. Nauk SSSR Ser. Khim. 1987 1969 (in Russian) (Chem. Abstr. 1988 108 204147m). 7 D. V. Zagorevskii G. Ts. Hovsepyan and Z. V. Todres Izv.Akad. Nauk SSSR Ser. Khim. 1987 1182 (in Russian) (Chem. Abstr. 1988 108 204118c). 8 Z. V. Todres G. Ts. Hovsepyan A. Yu. Kosnikov S. V. Lindeman and Yu. T. Struchkov Zh. Org. Khim. 1988 24 2567 (in Russian) (Chem. Abstr. 1989 111 96744e). 9 Podgornova E. S. Lipina and V. V. Perekalin Zh. Org. Khim. 1975 11 213 (in Russian) (Chem. Abstr. 1975 82 139464r). 10 H. Shechter J. J. Gardikes T. S. Cantrell and G. V. D. Tiers J. Am. Chem. Soc. 1967 89 3005. Paper 6/04933H Received 15th July 1996 Accepted 23rd October 1996 J. Chem. Soc. Perkin Trans. 1 1997 747 First examples of arylazo derivatives of cyclooctatetraene † Zori V. Todres and Ghevork Ts. Hovsepyan Research Institute The Cleveland Clinic Foundation 4075 Monticello Boulevard #205A Cleveland Ohio 44121 USA Disodium and dipotassium derivatives of 1,6-dinitrocyclooctatetraene (substrates) react with benzenediazo compounds (reagents) in THF to yield bis(azo)- or nitro(azo)-cyclooctatetraenes the first cyclooctatetraene arylazo derivatives.Structures of the azo compounds are established by conventional methods and confirmed by X-ray crystallography. Together with the main products of electrophilic substitution products of substrate-to-reagent electron transfer are formed. The electron-transfer products predominate with DMSO instead of THF as a solvent. The difference is apparently a result of ion-pair disintegration in the case of the substrate reactions when DMSO a strong dissociating solvent is used. Introduction The present work describes the study of alkali metal compounds of nitro and azoxy derivatives which exhibit distinct organometallic character and differ fundamentally in reactivity from their respective anion-radicals and dianions which have separate alkali-metal counterions.2,3 Here we focus on the disodium and dipotassium derivatives of 1,6-dinitrocycloocta- 1,3,5,7-tetraene 1.The neutral molecule of 1 has a boat conformation with the two nitro groups located above the boat.4 For the di(Na/K) derivative of 1 planar and non-planar structures are theoretically possible. The planar form 2 is characterized by delocalization of the two excess electrons in the eight-membered ring. The same manner of delocalization is characteristic for the di(Na/K) derivative of unsubstituted cyclooctatetraene (COT) and dimethyl-COT.5 The non-planar form 3 requires fixation of the two excess electrons at the two nitro groups blocked by two alkali metals (see Scheme 1).Conditions for existence of forms 2 and 3 The di(Na/K) derivatives of 1 were prepared by means of interchange between 1 and di(Na/K) derivatives of COT in tetrahydrofuran (THF). An alternative approach consisted of treatment of 1,4-dinitrocycloocta-2,5,7-triene with (Na/K) methoxides in methanol. By means of spectral [IR NMR (1H 13C)] methods we earlier found that form 3 became stable in non-dissociating solvents.6 In other words the salts of the dianion of 1 exist in the form of ion pairs and the excess negative charges are localized primarily on the nitro groups. In dissociating solvents the ion pairs are broken up and free ions are formed. This leads to a considerable shift of electron density in the eight-membered ring see structure 2.6 We had concluded in our earlier work6 that the difference between forms 2 and 3 must be reflected in their reactivity.The increase in delocalization of the excess electrons which is a consequence of dissociation of the ion pairs must lead to an increase in the level of the donor properties of the substrates. Thus when the free dianion 2 is treated with electrophiles it will more readily give up electrons than it will enter into electrophilic substitution. The characteristic reaction of electrophilic substitution of an aci-nitro group (NOO2M+) in contrast should proceed more readily in non-dissociating solvents when the substrates act as the ion pairs 3.6 † This work was initially presented in the VI International Conference on Organic Synthesis.1 The aim of our present study was to verify the prediction for the case of azo coupling and if successful to obtain new arylazo derivatives of cyclooctatetraene.Interaction between di(Na/K) derivatives of 1 and benzenediazo cations In THF or 1,2-dimethoxyethane (DME) the disodium or dipotassium derivative of 1 reacts with benzenediazo cations in two ways. One of them the minor is one-electron reduction of the cations. It results in N2 evolution and formation of 1 and benzene derivatives RC6H5 (see Scheme 2 and Table 1). This reaction proceeds to 10–20% only whereas the main route is the formation of bis(azo) and nitro(azo) derivatives of COT. All appearances suggest that the key stage of the reaction is ipso-coupling with intermediates 4 and 5 probably being formed (see Scheme 3).Alkali nitrite is cleaved from the intermediate 4 while dinitrogen tetroxide is liberated from the intermediate 5. At the same time the cyclooctatriene ring is transformed into a cyclooctatetraene ring to give the final products 6 and 7. Transformation of 5 into 6 is also possible (with elimination of p-RC6H4N2NO2). Mono 6a–c and bis(azo) derivatives 7a–c are obtained together irrespective of the stoichiometric relationship between the reagents and the substrate. Under similar conditions yields Scheme 1 NO2 O2N O2N NO2 = M+ M+ MOON NOOM +2e +2M+ +2e +2M+ 2 1 3 M = Na K 748 J. Chem. Soc. Perkin Trans. 1 1997 of nitroazo compounds 6 increase and yields of bis(azo) compounds 7 decrease along with a decrease in the acceptor ability of the substituent R in the benzenediazo cation.Where R ]] NMe2 only monosubstitution takes place with formation of product 6d. All the above mentioned data are collected in Table 1. The coupling activity of aryldiazo cations drops with a change of R from acceptor to donor. The 1-nitro-6-benzeneazo derivatives 6a–d and 1,6-bis- (benzeneazo) derivatives 7a–c formed are crystals with bright colours from yellow to brown. They are air-stable soluble in organic solvents (acetone benzene chloroform) and have sharp mps (see Tables 2 and 3). Elemental analytical results are compatible with the structural formulae of 6 and 7. The mass spectra of all the compounds prepared show molecular ion peaks (M~+) with intensities in the range 0.4–5% of the total ion current. The major fragmentation pathways for the M~+ are related to cleavage of the bonds between the nitrogen and carbon atoms of the Scheme 2 2 + 2 ( p -RC6H4N2BF4) –2 (MBF4) O2N NO2 + 2 [ p -RC6H4N2 • ] ; 1 [ p -RC6H4N2 • ] [ p -RC6H4 • ] RC6H5 +H• –N2 M = Na K; R = NO2 SCN OMe NMe2 Scheme 3 MOON O2N O2N N2Ar N2Ar ArN2 O2N –MNO2 N2Ar 4 NO2 6 Ar = p-RC6H4 ArN2 N2Ar M = Na K; R = a NO2; b SCN; c OMe; d NMe2 7 5 –N2O4 Ar = p-RC6H4 R = a NO2; b SCN; c OMe; Table 1 Interaction between disodium 1,6-dinitrocyclooctatetraene and tetrafluoroborates of diazo cations with general formula p- RC6H4N2BF4 (substrate reagent ratio 1 2; reaction temperature is 25 8C) Yield (%) Reagent (R) Solvent N2 RPh 1 6 7 NMe2 OMe SCN NO2 THF DMSO THF THF THF DMSO 8 42 12 18 22 71 6 21 4 15 18 53 4 36 5 14 14 52 88 27 57 38 30 6 00 26 34 39 4 COT rings; this corresponds to elimination of (M-NO2)+ and (M-RC6H4N2)+ fragments.Peaks of the (RC6H4)+ ion are the most intense in each case.7 Our preliminary work7 gives a full interpretation of the mass spectra of compounds 6 and 7. From the 1H NMR spectra of compounds 6 and 7 it was possible to identify the AA9 BB9 signals of the phenyl protons with their characteristic 9 Hz coupling; similarly signals from the proton-containing benzene substituents were also identifi- able (see Table 2). The eight-membered ring protons however showed broad signals in the region of d 6–8. The line widening resulted from very fast interchange between the 1,6- and 1,4- valence isomers at ambient temperature (25 8C). To complete the structural proof an X-ray analysis was performed for 1-nitro-6-(4-thiocyanatobenzeneazo)cycloocta- 1,3,5,7-tetraene as a typical example.Published separately,4 the structure is depicted in Fig. 1. The formation of the products in Scheme 3 have also been demonstrated. Sodium or potassium nitrite was shown to be present by IR spectroscopy in the residue from the reaction. The presence of dinitrogen tetroxide in the reaction mixture leads to formation of tarry products as minor components. The formation of N2O4 was revealed by the radical nitration of a minor electron-transfer product when disodium 1,6-dinitrocyclooctatetraene reacted with p-methoxybenzenediazonium tetrafluoroborate (in air THF as a solvent) to give a new nitro compound (see Scheme 4). Product 8 was isolated in 6% yield and its structure was established by X-ray analysis.8 p-Methoxyphenyl radicals (produced by electron transfer to the diazo cation from the disodium derivative of 1) are likely to form p-methoxyphenol after aerial oxidation.This then scavenges dinitrogen tetroxide to give 4-methoxy-2-nitrophenol 8. ortho-Nitration with respect to the hydroxy group rather than the methoxy group is preferred because of stabilization of the final product 8 by intramolecular hydrogen bonding between the NO2 and OH. If the reaction is conducted under argon nitro-product formation is suppressed. It is unnecessary to conduct the reaction between the dialkali compound 1 and a diazo salt under an argon atmosphere. Moreover without an argon flow it is possible to collect and estimate the volume of nitrogen evolved. The reaction was considered to be complete when the evolution of nitrogen gas had ceased.As seen from Table 1 the maximum yield of nitrogen (22%) is observed for the substrate p-NO2C6H4N2BF4 whilst the minimum (8%) occurs for the substrate p-Me2NC6H4N2BF4. Substrates with para substituents OMe and SCN occupy a middle position (12 and 18%). All comparisons are referred to with THF as the solvent. With DMSO instead of THF there is a sharp increase in nitrogen elimination along with yields of RC6H5. At the same Fig. 1 J. Chem. Soc. Perkin Trans. 1 1997 749 Table 2 Cyclooctatetraene azo compounds obtained according to Table 1 Mp/8C Empirical Azo compound R [solvent] Found (%) formula Calc. (%) dH/ppm 6a 6b 6c 6d 7a 7b 7c NO2 SCN OMe NMe2 NO2 SCN OMe 170 [benzene] 131.5 [benzene] 122.5 [diethyl ether] 152.5 [ethyl acetate] 186 [benzene] 201 [acetone] 178 with decomp.[benzene] C 56.17 H 3.41 N 18.80 C 58.00 H 3.00 N 17.98 S 10.26 C 63.54 H 4.40 N 14.80 C 64.72 H 5.22 N 18.89 C 59.69 H 3.41 N 20.88 C 61.86 H 3.10 N 19.69 C 70.90 H 5.26 N 15.89 C14H10N4O4 C15H10N4O2S C15H13N3O3 C16H16N4O2 C20H14N6O4 C22H14N6S2 C22H20N4O2 C 56.37 H 3.53 N 18.79 C 58.06 H 3.23 N 18.06 S 10.32 C 63.60 H 4.59 N 14.84 C 64.86 H 5.41 N 18.92 C 59.70 H 3.48 N 20.90 C 61.97 H 3.29 N 19.72 C 70.97 H 5.38 N 15.05 8.44 (AA9 2H) 8.00 (BB9 2H) 7.94 (AA9 2H) 7.80 (BB9 2H) 7.83 (BB9 2H) 7.08 (AA9 2H) 3.93 (OMe s 3H) 7.56 (BB9 2H) 6.80 (AA9 2H) 3.10 (NMe2 s 6H) 8.42 (AA9 4H) 8.00 (BB9 4H) 7.92 (AA9 4H) 7.80 (BB9 4H) 7.82 (BB9 4H) 7.08 (AA9 4H) 3.93 (OMe × 2 s 6H) time substitution is suppressed. There is a significant difference in the dissociating power of these two solvents (relative permittivities at 293 K are equal to 7.4 and 49 respectively).Experimental Preparation of dipotassium (disodium) 1,6-dinitro-COT Method 1. A filtered solution of freshly prepared dipotassium COT [from COT (1.04 g) and K (0.95 g)] in THF (40 ml) was added to a solution of 1,6-dinitro-COT (1.94 g 0.01 mol)9 in THF (20 ml) at 240 8C under argon. The reaction mixture was stirred at 240 8C for 30 min after which the temperature was raised to 25 8C. A yellow precipitate of 3 was formed and this was filtered off washed twice with cold THF and dried in vacuo over phosphorus pentoxide to yield a dry solid (2.6 g) (Found C 35.30; H 2.24; N 10.22; K 28.05. Calc. for C8H6K2N2O4 C 35.12; H 2.32; N 10.14; K 27.71%). The disodium derivative of 1,6-dinitro-COT was obtained in the same manner from disodium COT (Found C 40.22; H 2.31; N 11.53; Na 18.92.Calc. for C8H6N2Na2O4 C 40.00; H 2.50; N 11.67; Na 19.17%). Method 2. A solution of 1,4-dinitrocycloocta-2,5,7-triene 10 (1.96 g 0.01 mol) in THF (40 ml) was stirred with dry potassium methoxide (1.41 g 0.02 mol) at 220 8C for 20 min and then warmed to 25 8C over 30 min. Dipotassium 1,6- dinitro-COT was formed as a bright yellow precipitate which was treated as described above. The dry solid was obtained in 94% yield (2.55 g). The disodium analogue was prepared with sodium methoxide. The elemental composition and spectra of the (Na/K) derivatives obtained by methods 1 and 2 were identical. In method 2 1,4-dinitrocyclooctatriene used as a starting Table 3 Absorption bands in the electronic spectra of cyclooctatetraene azo compounds obtained according to Table 1 Azo compound R lmax/nm e × 104/l mol21 cm21 6a 6b 6c 6d 7a 7b 7c NO2 SCN OMe NMe2 NO2 SCN OMe 306 356 236 323 248 342 257 460 304 364 236 322 398 250 342 400 2.20 1.42 0.88 1.06 1.74 1.95 1.46 2.10 3.60 2.04 1.76 2.22 1.25 2.22 3.06 2.76 material was synthesized by nitration of COT with N2O4.The resultant compound was purified by procedures given in ref. 10 to give white crystals which were dried in vacuo (no more than 1 h). Interaction between the dipotassium or disodium derivative of 1,6- dinitro-COT and benzenediazonium tetrafluoroborates a typical procedure A dry tetrafluoroborate (0.01 mol) was slowly added to a suspension of the dipotassium derivative 3 (1.36 g) or disodium derivative 3 (1.20 g 0.05 mol) in THF or DME (40 ml). When DMSO was used as a solvent 10 ml were utilized to dissolve substrate 3 and 20 ml to dissolve the diazo salt.The reaction mixture was stirred over 30 min at 25 8C. Nitrogen was evolved in the course of the reaction and when this ceased the reaction Scheme 4 N2 + MeO N2 • MeO MeO OO• MeO OOH MeO + e OH MeO –N2 • +O2 +H• OH MeO +N2O4 –1/2 O2 NO2 –HNO2 8 750 J. Chem. Soc. Perkin Trans. 1 1997 mixture was stirred for a further 30 min and then filtered; a small quantity of this filtrate was examined by GLC (see below). The remaining filtrate was concentrated to 25% of its original volume. The resulting precipitate was collected and in solution subjected to chromatography (22 × 600 mm silica gel column; eluent hexane–ethyl acetate 3 1). The solid resulting from filtration of the reaction mixture was treated with cold acetone (3 × 10 ml) dried and analysed by means of IR spectroscopy and qualitative analytical methods.The salts MNO2 and MBF4 (M ]] Na K) were shown to be components of the solid although their yields were not determined. The yields of 1,6-dinitro-COT 1 its azo derivatives 6 and 7 nitrogen gas and benzenes RC6H5 are given in Table 1. Tables 2 and 3 show the analytical data upon which identification of the azo products 6 and 7 was established. Quantities of RC6H5 were determined by a GLC method with authentic standard materials introduced into the mixtures being analysed. Nitrogen was used as a carrier gas in all cases. For anisole and N,N-dimethylaniline a stainless-steel column (3 × 3700 mm) was used. The stationary phase was PEG-20M on silanized Chromatone N-AW 40–60 mesh.For phenyl thiocyanate and nitrobenzene a glass column (2 × 2000 mm) was employed. In this case the stationary phase was 5% SE-30 on silanized Chromatone N-AW-DMCS 20–25 mesh. 1H NMR Spectra were obtained on a Bruker WP-200 instrument using (CD3)2CO as a solvent with SiMe4 as a standard. Electronic absorption spectra were recorded using a Specord UV–VIS spectrometer and a cuvette of 1 cm diameter with MeOH as solvent and with 1023 mol l21 concentrations of the azo compounds. References 1 Z. V. Todres G. Ts. Hovsepyan in Abstracts of papers of the VI International Conference on Organic Synthesis August 10–15 1986 Moscow Russia. 2 Z. V. Todres J. Organomet. Chem. 1992 441 349. 3 Z. V. Todres S. P. Avagyan and D. N. Kursanov J. Organomet. Chem. 1975 97 139.4 Z. V. Todres G. Ts. Hovsepyan V. I. Bakhmutov A. Yu. Kosnikov S. V. Lindeman and Yu. T. Struchkov Zh. Org. Khim. 1989 25 75 (in Russian) (Chem. Abstr. 1989 111 77532t). 5 G. J. Fray and R. G. Saxton The Chemistry of Cyclo-octatetraene and Its Derivatives Cambridge University Press London 1978 p. 48. 6 Z. V. Todres G. Ts. Hovsepyan I. A. Garbuzova I. V. Stankevich and V. I. Bakhmutov Izv. Akad. Nauk SSSR Ser. Khim. 1987 1969 (in Russian) (Chem. Abstr. 1988 108 204147m). 7 D. V. Zagorevskii G. Ts. Hovsepyan and Z. V. Todres Izv. Akad. Nauk SSSR Ser. Khim. 1987 1182 (in Russian) (Chem. Abstr. 1988 108 204118c). 8 Z. V. Todres G. Ts. Hovsepyan A. Yu. Kosnikov S. V. Lindeman and Yu. T. Struchkov Zh. Org. Khim. 1988 24 2567 (in Russian) (Chem. Abstr. 1989 111 96744e). 9 Podgornova E.S. Lipina and V. V. Perekalin Zh. Org. Khim. 1975 11 213 (in Russian) (Chem. Abstr. 1975 82 139464r). 10 H. Shechter J. J. Gardikes T. S. Cantrell and G. V. D. Tiers J. Am. Chem. Soc. 1967 89 3005. Paper 6/04933H Received 15th July 1996 Accepted 23rd October 1996 J. Chem. Soc. Perkin Trans. 1 1997 747 First examples of arylazo derivatives of cyclooctatetraene † Zori V. Todres and Ghevork Ts. Hovsepyan Research Institute The Cleveland Clinic Foundation 4075 Monticello Boulevard #205A Cleveland Ohio 44121 USA Disodium and dipotassium derivatives of 1,6-dinitrocyclooctatetraene (substrates) react with benzenediazo compounds (reagents) in THF to yield bis(azo)- or nitro(azo)-cyclooctatetraenes the first cyclooctatetraene arylazo derivatives. Structures of the azo compounds are established by conventional methods and confirmed by X-ray crystallography.Together with the main products of electrophilic substitution products of substrate-to-reagent electron transfer are formed. The electron-transfer products predominate with DMSO instead of THF as a solvent. The difference is apparently a result of ion-pair disintegration in the case of the substrate reactions when DMSO a strong dissociating solvent is used. Introduction The present work describes the study of alkali metal compounds of nitro and azoxy derivatives which exhibit distinct organometallic character and differ fundamentally in reactivity from their respective anion-radicals and dianions which have separate alkali-metal counterions.2,3 Here we focus on the disodium and dipotassium derivatives of 1,6-dinitrocycloocta- 1,3,5,7-tetraene 1.The neutral molecule of 1 has a boat conformation with the two nitro groups located above the boat.4 For the di(Na/K) derivative of 1 planar and non-planar structures are theoretically possible. The planar form 2 is characterized by delocalization of the two excess electrons in the eight-membered ring. The same manner of delocalization is characteristic for the di(Na/K) derivative of unsubstituted cyclooctatetraene (COT) and dimethyl-COT.5 The non-planar form 3 requires fixation of the two excess electrons at the two nitro groups blocked by two alkali metals (see Scheme 1). Conditions for existence of forms 2 and 3 The di(Na/K) derivatives of 1 were prepared by means of interchange between 1 and di(Na/K) derivatives of COT in tetrahydrofuran (THF).An alternative approach consisted of treatment of 1,4-dinitrocycloocta-2,5,7-triene with (Na/K) methoxides in methanol. By means of spectral [IR NMR (1H 13C)] methods we earlier found that form 3 became stable in non-dissociating solvents.6 In other words the salts of the dianion of 1 exist in the form of ion pairs and the excess negative charges are localized primarily on the nitro groups. In dissociating solvents the ion pairs are broken up and free ions are formed. This leads to a considerable shift of electron density in the eight-membered ring see structure 2.6 We had concluded in our earlier work6 that the difference between forms 2 and 3 must be reflected in their reactivity. The increase in delocalization of the excess electrons which is a consequence of dissociation of the ion pairs must lead to an increase in the level of the donor properties of the substrates.Thus when the free dianion 2 is treated with electrophiles it will more readily give up electrons than it will enter into electrophilic substitution. The characteristic reaction of electrophilic substitution of an aci-nitro group (NOO2M+) in contrast should proceed more readily in non-dissociating solvents when the substrates act as the ion pairs 3.6 † This work was initially presented in the VI International Conference on Organic Synthesis.1 The aim of our present study was to verify the prediction for the case of azo coupling and if successful to obtain new arylazo derivatives of cyclooctatetraene. Interaction between di(Na/K) derivatives of 1 and benzenediazo cations In THF or 1,2-dimethoxyethane (DME) the disodium or dipotassium derivative of 1 reacts with benzenediazo cations in two ways.One of them the minor is one-electron reduction of the cations. It results in N2 evolution and formation of 1 and benzene derivatives RC6H5 (see Scheme 2 and Table 1). This reaction proceeds to 10–20% only whereas the main route is the formation of bis(azo) and nitro(azo) derivatives of COT. All appearances suggest that the key stage of the reaction is ipso-coupling with intermediates 4 and 5 probably being formed (see Scheme 3). Alkali nitrite is cleaved from the intermediate 4 while dinitrogen tetroxide is liberated from the intermediate 5. At the same time the cyclooctatriene ring is transformed into a cyclooctatetraene ring to give the final products 6 and 7. Transformation of 5 into 6 is also possible (with elimination of p-RC6H4N2NO2).Mono 6a–c and bis(azo) derivatives 7a–c are obtained together irrespective of the stoichiometric relationship between the reagents and the substrate. Under similar conditions yields Scheme 1 NO2 O2N O2N NO2 = M+ M+ MOON NOOM +2e +2M+ +2e +2M+ 2 1 3 M = Na K 748 J. Chem. Soc. Perkin Trans. 1 1997 of nitroazo compounds 6 increase and yields of bis(azo) compounds 7 decrease along with a decrease in the acceptor ability of the substituent R in the benzenediazo cation. Where R ]] NMe2 only monosubstitution takes place with formation of product 6d. All the above mentioned data are collected in Table 1. The coupling activity of aryldiazo cations drops with a change of R from acceptor to donor. The 1-nitro-6-benzeneazo derivatives 6a–d and 1,6-bis- (benzeneazo) derivatives 7a–c formed are crystals with bright colours from yellow to brown.They are air-stable soluble in organic solvents (acetone benzene chloroform) and have sharp mps (see Tables 2 and 3). Elemental analytical results are compatible with the structural formulae of 6 and 7. The mass spectra of all the compounds prepared show molecular ion peaks (M~+) with intensities in the range 0.4–5% of the total ion current. The major fragmentation pathways for the M~+ are related to cleavage of the bonds between the nitrogen and carbon atoms of the Scheme 2 2 + 2 ( p -RC6H4N2BF4) –2 (MBF4) O2N NO2 + 2 [ p -RC6H4N2 • ] ; 1 [ p -RC6H4N2 • ] [ p -RC6H4 • ] RC6H5 +H• –N2 M = Na K; R = NO2 SCN OMe NMe2 Scheme 3 MOON O2N O2N N2Ar N2Ar ArN2 O2N –MNO2 N2Ar 4 NO2 6 Ar = p-RC6H4 ArN2 N2Ar M = Na K; R = a NO2; b SCN; c OMe; d NMe2 7 5 –N2O4 Ar = p-RC6H4 R = a NO2; b SCN; c OMe; Table 1 Interaction between disodium 1,6-dinitrocyclooctatetraene and tetrafluoroborates of diazo cations with general formula p- RC6H4N2BF4 (substrate reagent ratio 1 2; reaction temperature is 25 8C) Yield (%) Reagent (R) Solvent N2 RPh 1 6 7 NMe2 OMe SCN NO2 THF DMSO THF THF THF DMSO 8 42 12 18 22 71 6 21 4 15 18 53 4 36 5 14 14 52 88 27 57 38 30 6 00 26 34 39 4 COT rings; this corresponds to elimination of (M-NO2)+ and (M-RC6H4N2)+ fragments.Peaks of the (RC6H4)+ ion are the most intense in each case.7 Our preliminary work7 gives a full interpretation of the mass spectra of compounds 6 and 7. From the 1H NMR spectra of compounds 6 and 7 it was possible to identify the AA9 BB9 signals of the phenyl protons with their characteristic 9 Hz coupling; similarly signals from the proton-containing benzene substituents were also identifi- able (see Table 2).The eight-membered ring protons however showed broad signals in the region of d 6–8. The line widening resulted from very fast interchange between the 1,6- and 1,4- valence isomers at ambient temperature (25 8C). To complete the structural proof an X-ray analysis was performed for 1-nitro-6-(4-thiocyanatobenzeneazo)cycloocta- 1,3,5,7-tetraene as a typical example. Published separately,4 the structure is depicted in Fig. 1. The formation of the products in Scheme 3 have also been demonstrated. Sodium or potassium nitrite was shown to be present by IR spectroscopy in the residue from the reaction.The presence of dinitrogen tetroxide in the reaction mixture leads to formation of tarry products as minor components. The formation of N2O4 was revealed by the radical nitration of a minor electron-transfer product when disodium 1,6-dinitrocyclooctatetraene reacted with p-methoxybenzenediazonium tetrafluoroborate (in air THF as a solvent) to give a new nitro compound (see Scheme 4). Product 8 was isolated in 6% yield and its structure was established by X-ray analysis.8 p-Methoxyphenyl radicals (produced by electron transfer to the diazo cation from the disodium derivative of 1) are likely to form p-methoxyphenol after aerial oxidation. This then scavenges dinitrogen tetroxide to give 4-methoxy-2-nitrophenol 8. ortho-Nitration with respect to the hydroxy group rather than the methoxy group is preferred because of stabilization of the final product 8 by intramolecular hydrogen bonding between the NO2 and OH.If the reaction is conducted under argon nitro-product formation is suppressed. It is unnecessary to conduct the reaction between the dialkali compound 1 and a diazo salt under an argon atmosphere. Moreover without an argon flow it is possible to collect and estimate the volume of nitrogen evolved. The reaction was considered to be complete when the evolution of nitrogen gas had ceased. As seen from Table 1 the maximum yield of nitrogen (22%) is observed for the substrate p-NO2C6H4N2BF4 whilst the minimum (8%) occurs for the substrate p-Me2NC6H4N2BF4. Substrates with para substituents OMe and SCN occupy a middle position (12 and 18%). All comparisons are referred to with THF as the solvent.With DMSO instead of THF there is a sharp increase in nitrogen elimination along with yields of RC6H5. At the same Fig. 1 J. Chem. Soc. Perkin Trans. 1 1997 749 Table 2 Cyclooctatetraene azo compounds obtained according to Table 1 Mp/8C Empirical Azo compound R [solvent] Found (%) formula Calc. (%) dH/ppm 6a 6b 6c 6d 7a 7b 7c NO2 SCN OMe NMe2 NO2 SCN OMe 170 [benzene] 131.5 [benzene] 122.5 [diethyl ether] 152.5 [ethyl acetate] 186 [benzene] 201 [acetone] 178 with decomp. [benzene] C 56.17 H 3.41 N 18.80 C 58.00 H 3.00 N 17.98 S 10.26 C 63.54 H 4.40 N 14.80 C 64.72 H 5.22 N 18.89 C 59.69 H 3.41 N 20.88 C 61.86 H 3.10 N 19.69 C 70.90 H 5.26 N 15.89 C14H10N4O4 C15H10N4O2S C15H13N3O3 C16H16N4O2 C20H14N6O4 C22H14N6S2 C22H20N4O2 C 56.37 H 3.53 N 18.79 C 58.06 H 3.23 N 18.06 S 10.32 C 63.60 H 4.59 N 14.84 C 64.86 H 5.41 N 18.92 C 59.70 H 3.48 N 20.90 C 61.97 H 3.29 N 19.72 C 70.97 H 5.38 N 15.05 8.44 (AA9 2H) 8.00 (BB9 2H) 7.94 (AA9 2H) 7.80 (BB9 2H) 7.83 (BB9 2H) 7.08 (AA9 2H) 3.93 (OMe s 3H) 7.56 (BB9 2H) 6.80 (AA9 2H) 3.10 (NMe2 s 6H) 8.42 (AA9 4H) 8.00 (BB9 4H) 7.92 (AA9 4H) 7.80 (BB9 4H) 7.82 (BB9 4H) 7.08 (AA9 4H) 3.93 (OMe × 2 s 6H) time substitution is suppressed.There is a significant difference in the dissociating power of these two solvents (relative permittivities at 293 K are equal to 7.4 and 49 respectively). Experimental Preparation of dipotassium (disodium) 1,6-dinitro-COT Method 1. A filtered solution of freshly prepared dipotassium COT [from COT (1.04 g) and K (0.95 g)] in THF (40 ml) was added to a solution of 1,6-dinitro-COT (1.94 g 0.01 mol)9 in THF (20 ml) at 240 8C under argon.The reaction mixture was stirred at 240 8C for 30 min after which the temperature was raised to 25 8C. A yellow precipitate of 3 was formed and this was filtered off washed twice with cold THF and dried in vacuo over phosphorus pentoxide to yield a dry solid (2.6 g) (Found C 35.30; H 2.24; N 10.22; K 28.05. Calc. for C8H6K2N2O4 C 35.12; H 2.32; N 10.14; K 27.71%). The disodium derivative of 1,6-dinitro-COT was obtained in the same manner from disodium COT (Found C 40.22; H 2.31; N 11.53; Na 18.92. Calc. for C8H6N2Na2O4 C 40.00; H 2.50; N 11.67; Na 19.17%). Method 2. A solution of 1,4-dinitrocycloocta-2,5,7-triene 10 (1.96 g 0.01 mol) in THF (40 ml) was stirred with dry potassium methoxide (1.41 g 0.02 mol) at 220 8C for 20 min and then warmed to 25 8C over 30 min.Dipotassium 1,6- dinitro-COT was formed as a bright yellow precipitate which was treated as described above. The dry solid was obtained in 94% yield (2.55 g). The disodium analogue was prepared with sodium methoxide. The elemental composition and spectra of the (Na/K) derivatives obtained by methods 1 and 2 were identical. In method 2 1,4-dinitrocyclooctatriene used as a starting Table 3 Absorption bands in the electronic spectra of cyclooctatetraene azo compounds obtained according to Table 1 Azo compound R lmax/nm e × 104/l mol21 cm21 6a 6b 6c 6d 7a 7b 7c NO2 SCN OMe NMe2 NO2 SCN OMe 306 356 236 323 248 342 257 460 304 364 236 322 398 250 342 400 2.20 1.42 0.88 1.06 1.74 1.95 1.46 2.10 3.60 2.04 1.76 2.22 1.25 2.22 3.06 2.76 material was synthesized by nitration of COT with N2O4.The resultant compound was purified by procedures given in ref. 10 to give white crystals which were dried in vacuo (no more than 1 h). Interaction between the dipotassium or disodium derivative of 1,6- dinitro-COT and benzenediazonium tetrafluoroborates a typical procedure A dry tetrafluoroborate (0.01 mol) was slowly added to a suspension of the dipotassium derivative 3 (1.36 g) or disodium derivative 3 (1.20 g 0.05 mol) in THF or DME (40 ml). When DMSO was used as a solvent 10 ml were utilized to dissolve substrate 3 and 20 ml to dissolve the diazo salt. The reaction mixture was stirred over 30 min at 25 8C. Nitrogen was evolved in the course of the reaction and when this ceased the reaction Scheme 4 N2 + MeO N2 • MeO MeO OO• MeO OOH MeO + e OH MeO –N2 • +O2 +H• OH MeO +N2O4 –1/2 O2 NO2 –HNO2 8 750 J.Chem. Soc. Perkin Trans. 1 1997 mixture was stirred for a further 30 min and then filtered; a small quantity of this filtrate was examined by GLC (see below). The remaining filtrate was concentrated to 25% of its original volume. The resulting precipitate was collected and in solution subjected to chromatography (22 × 600 mm silica gel column; eluent hexane–ethyl acetate 3 1). The solid resulting from filtration of the reaction mixture was treated with cold acetone (3 × 10 ml) dried and analysed by means of IR spectroscopy and qualitative analytical methods. The salts MNO2 and MBF4 (M ]] Na K) were shown to be components of the solid although their yields were not determined.The yields of 1,6-dinitro-COT 1 its azo derivatives 6 and 7 nitrogen gas and benzenes RC6H5 are given in Table 1. Tables 2 and 3 show the analytical data upon which identification of the azo products 6 and 7 was established. Quantities of RC6H5 were determined by a GLC method with authentic standard materials introduced into the mixtures being analysed. Nitrogen was used as a carrier gas in all cases. For anisole and N,N-dimethylaniline a stainless-steel column (3 × 3700 mm) was used. The stationary phase was PEG-20M on silanized Chromatone N-AW 40–60 mesh. For phenyl thiocyanate and nitrobenzene a glass column (2 × 2000 mm) was employed. In this case the stationary phase was 5% SE-30 on silanized Chromatone N-AW-DMCS 20–25 mesh. 1H NMR Spectra were obtained on a Bruker WP-200 instrument using (CD3)2CO as a solvent with SiMe4 as a standard.Electronic absorption spectra were recorded using a Specord UV–VIS spectrometer and a cuvette of 1 cm diameter with MeOH as solvent and with 1023 mol l21 concentrations of the azo compounds. References 1 Z. V. Todres G. Ts. Hovsepyan in Abstracts of papers of the VI International Conference on Organic Synthesis August 10–15 1986 Moscow Russia. 2 Z. V. Todres J. Organomet. Chem. 1992 441 349. 3 Z. V. Todres S. P. Avagyan and D. N. Kursanov J. Organomet. Chem. 1975 97 139. 4 Z. V. Todres G. Ts. Hovsepyan V. I. Bakhmutov A. Yu. Kosnikov S. V. Lindeman and Yu. T. Struchkov Zh. Org. Khim. 1989 25 75 (in Russian) (Chem. Abstr. 1989 111 77532t). 5 G. J. Fray and R. G. Saxton The Chemistry of Cyclo-octatetraene and Its Derivatives Cambridge University Press London 1978 p.48. 6 Z. V. Todres G. Ts. Hovsepyan I. A. Garbuzova I. V. Stankevich and V. I. Bakhmutov Izv. Akad. Nauk SSSR Ser. Khim. 1987 1969 (in Russian) (Chem. Abstr. 1988 108 204147m). 7 D. V. Zagorevskii G. Ts. Hovsepyan and Z. V. Todres Izv. Akad. Nauk SSSR Ser. Khim. 1987 1182 (in Russian) (Chem. Abstr. 1988 108 204118c). 8 Z. V. Todres G. Ts. Hovsepyan A. Yu. Kosnikov S. V. Lindeman and Yu. T. Struchkov Zh. Org. Khim. 1988 24 2567 (in Russian) (Chem. Abstr. 1989 111 96744e). 9 Podgornova E. S. Lipina and V. V. Perekalin Zh. Org. Khim. 1975 11 213 (in Russian) (Chem. Abstr. 1975 82 139464r). 10 H. Shechter J. J. Gardikes T. S. Cantrell and G. V. D. Tiers J. Am. Chem. Soc. 1967 89 3005. Paper 6/04933H Received 15th July 1996 Accepted 23rd October 1996 J.Chem. Soc. Perkin Trans. 1 1997 747 First examples of arylazo derivatives of cyclooctatetraene † Zori V. Todres and Ghevork Ts. Hovsepyan Research Institute The Cleveland Clinic Foundation 4075 Monticello Boulevard #205A Cleveland Ohio 44121 USA Disodium and dipotassium derivatives of 1,6-dinitrocyclooctatetraene (substrates) react with benzenediazo compounds (reagents) in THF to yield bis(azo)- or nitro(azo)-cyclooctatetraenes the first cyclooctatetraene arylazo derivatives. Structures of the azo compounds are established by conventional methods and confirmed by X-ray crystallography. Together with the main products of electrophilic substitution products of substrate-to-reagent electron transfer are formed. The electron-transfer products predominate with DMSO instead of THF as a solvent.The difference is apparently a result of ion-pair disintegration in the case of the substrate reactions when DMSO a strong dissociating solvent is used. Introduction The present work describes the study of alkali metal compounds of nitro and azoxy derivatives which exhibit distinct organometallic character and differ fundamentally in reactivity from their respective anion-radicals and dianions which have separate alkali-metal counterions.2,3 Here we focus on the disodium and dipotassium derivatives of 1,6-dinitrocycloocta- 1,3,5,7-tetraene 1. The neutral molecule of 1 has a boat conformation with the two nitro groups located above the boat.4 For the di(Na/K) derivative of 1 planar and non-planar structures are theoretically possible. The planar form 2 is characterized by delocalization of the two excess electrons in the eight-membered ring.The same manner of delocalization is characteristic for the di(Na/K) derivative of unsubstituted cyclooctatetraene (COT) and dimethyl-COT.5 The non-planar form 3 requires fixation of the two excess electrons at the two nitro groups blocked by two alkali metals (see Scheme 1). Conditions for existence of forms 2 and 3 The di(Na/K) derivatives of 1 were prepared by means of interchange between 1 and di(Na/K) derivatives of COT in tetrahydrofuran (THF). An alternative approach consisted of treatment of 1,4-dinitrocycloocta-2,5,7-triene with (Na/K) methoxides in methanol. By means of spectral [IR NMR (1H 13C)] methods we earlier found that form 3 became stable in non-dissociating solvents.6 In other words the salts of the dianion of 1 exist in the form of ion pairs and the excess negative charges are localized primarily on the nitro groups.In dissociating solvents the ion pairs are broken up and free ions are formed. This leads to a considerable shift of electron density in the eight-membered ring see structure 2.6 We had concluded in our earlier work6 that the difference between forms 2 and 3 must be reflected in their reactivity. The increase in delocalization of the excess electrons which is a consequence of dissociation of the ion pairs must lead to an increase in the level of the donor properties of the substrates. Thus when the free dianion 2 is treated with electrophiles it will more readily give up electrons than it will enter into electrophilic substitution. The characteristic reaction of electrophilic substitution of an aci-nitro group (NOO2M+) in contrast should proceed more readily in non-dissociating solvents when the substrates act as the ion pairs 3.6 † This work was initially presented in the VI International Conference on Organic Synthesis.1 The aim of our present study was to verify the prediction for the case of azo coupling and if successful to obtain new arylazo derivatives of cyclooctatetraene.Interaction between di(Na/K) derivatives of 1 and benzenediazo cations In THF or 1,2-dimethoxyethane (DME) the disodium or dipotassium derivative of 1 reacts with benzenediazo cations in two ways. One of them the minor is one-electron reduction of the cations. It results in N2 evolution and formation of 1 and benzene derivatives RC6H5 (see Scheme 2 and Table 1).This reaction proceeds to 10–20% only whereas the main route is the formation of bis(azo) and nitro(azo) derivatives of COT. All appearances suggest that the key stage of the reaction is ipso-coupling with intermediates 4 and 5 probably being formed (see Scheme 3). Alkali nitrite is cleaved from the intermediate 4 while dinitrogen tetroxide is liberated from the intermediate 5. At the same time the cyclooctatriene ring is transformed into a cyclooctatetraene ring to give the final products 6 and 7. Transformation of 5 into 6 is also possible (with elimination of p-RC6H4N2NO2). Mono 6a–c and bis(azo) derivatives 7a–c are obtained together irrespective of the stoichiometric relationship between the reagents and the substrate. Under similar conditions yields Scheme 1 NO2 O2N O2N NO2 = M+ M+ MOON NOOM +2e +2M+ +2e +2M+ 2 1 3 M = Na K 748 J.Chem. Soc. Perkin Trans. 1 1997 of nitroazo compounds 6 increase and yields of bis(azo) compounds 7 decrease along with a decrease in the acceptor ability of the substituent R in the benzenediazo cation. Where R ]] NMe2 only monosubstitution takes place with formation of product 6d. All the above mentioned data are collected in Table 1. The coupling activity of aryldiazo cations drops with a change of R from acceptor to donor. The 1-nitro-6-benzeneazo derivatives 6a–d and 1,6-bis- (benzeneazo) derivatives 7a–c formed are crystals with bright colours from yellow to brown. They are air-stable soluble in organic solvents (acetone benzene chloroform) and have sharp mps (see Tables 2 and 3). Elemental analytical results are compatible with the structural formulae of 6 and 7.The mass spectra of all the compounds prepared show molecular ion peaks (M~+) with intensities in the range 0.4–5% of the total ion current. The major fragmentation pathways for the M~+ are related to cleavage of the bonds between the nitrogen and carbon atoms of the Scheme 2 2 + 2 ( p -RC6H4N2BF4) –2 (MBF4) O2N NO2 + 2 [ p -RC6H4N2 • ] ; 1 [ p -RC6H4N2 • ] [ p -RC6H4 • ] RC6H5 +H• –N2 M = Na K; R = NO2 SCN OMe NMe2 Scheme 3 MOON O2N O2N N2Ar N2Ar ArN2 O2N –MNO2 N2Ar 4 NO2 6 Ar = p-RC6H4 ArN2 N2Ar M = Na K; R = a NO2; b SCN; c OMe; d NMe2 7 5 –N2O4 Ar = p-RC6H4 R = a NO2; b SCN; c OMe; Table 1 Interaction between disodium 1,6-dinitrocyclooctatetraene and tetrafluoroborates of diazo cations with general formula p- RC6H4N2BF4 (substrate reagent ratio 1 2; reaction temperature is 25 8C) Yield (%) Reagent (R) Solvent N2 RPh 1 6 7 NMe2 OMe SCN NO2 THF DMSO THF THF THF DMSO 8 42 12 18 22 71 6 21 4 15 18 53 4 36 5 14 14 52 88 27 57 38 30 6 00 26 34 39 4 COT rings; this corresponds to elimination of (M-NO2)+ and (M-RC6H4N2)+ fragments.Peaks of the (RC6H4)+ ion are the most intense in each case.7 Our preliminary work7 gives a full interpretation of the mass spectra of compounds 6 and 7. From the 1H NMR spectra of compounds 6 and 7 it was possible to identify the AA9 BB9 signals of the phenyl protons with their characteristic 9 Hz coupling; similarly signals from the proton-containing benzene substituents were also identifi- able (see Table 2). The eight-membered ring protons however showed broad signals in the region of d 6–8.The line widening resulted from very fast interchange between the 1,6- and 1,4- valence isomers at ambient temperature (25 8C). To complete the structural proof an X-ray analysis was performed for 1-nitro-6-(4-thiocyanatobenzeneazo)cycloocta- 1,3,5,7-tetraene as a typical example. Published separately,4 the structure is depicted in Fig. 1. The formation of the products in Scheme 3 have also been demonstrated. Sodium or potassium nitrite was shown to be present by IR spectroscopy in the residue from the reaction. The presence of dinitrogen tetroxide in the reaction mixture leads to formation of tarry products as minor components. The formation of N2O4 was revealed by the radical nitration of a minor electron-transfer product when disodium 1,6-dinitrocyclooctatetraene reacted with p-methoxybenzenediazonium tetrafluoroborate (in air THF as a solvent) to give a new nitro compound (see Scheme 4).Product 8 was isolated in 6% yield and its structure was established by X-ray analysis.8 p-Methoxyphenyl radicals (produced by electron transfer to the diazo cation from the disodium derivative of 1) are likely to form p-methoxyphenol after aerial oxidation. This then scavenges dinitrogen tetroxide to give 4-methoxy-2-nitrophenol 8. ortho-Nitration with respect to the hydroxy group rather than the methoxy group is preferred because of stabilization of the final product 8 by intramolecular hydrogen bonding between the NO2 and OH. If the reaction is conducted under argon nitro-product formation is suppressed. It is unnecessary to conduct the reaction between the dialkali compound 1 and a diazo salt under an argon atmosphere.Moreover without an argon flow it is possible to collect and estimate the volume of nitrogen evolved. The reaction was considered to be complete when the evolution of nitrogen gas had ceased. As seen from Table 1 the maximum yield of nitrogen (22%) is observed for the substrate p-NO2C6H4N2BF4 whilst the minimum (8%) occurs for the substrate p-Me2NC6H4N2BF4. Substrates with para substituents OMe and SCN occupy a middle position (12 and 18%). All comparisons are referred to with THF as the solvent. With DMSO instead of THF there is a sharp increase in nitrogen elimination along with yields of RC6H5. At the same Fig. 1 J. Chem. Soc. Perkin Trans. 1 1997 749 Table 2 Cyclooctatetraene azo compounds obtained according to Table 1 Mp/8C Empirical Azo compound R [solvent] Found (%) formula Calc.(%) dH/ppm 6a 6b 6c 6d 7a 7b 7c NO2 SCN OMe NMe2 NO2 SCN OMe 170 [benzene] 131.5 [benzene] 122.5 [diethyl ether] 152.5 [ethyl acetate] 186 [benzene] 201 [acetone] 178 with decomp. [benzene] C 56.17 H 3.41 N 18.80 C 58.00 H 3.00 N 17.98 S 10.26 C 63.54 H 4.40 N 14.80 C 64.72 H 5.22 N 18.89 C 59.69 H 3.41 N 20.88 C 61.86 H 3.10 N 19.69 C 70.90 H 5.26 N 15.89 C14H10N4O4 C15H10N4O2S C15H13N3O3 C16H16N4O2 C20H14N6O4 C22H14N6S2 C22H20N4O2 C 56.37 H 3.53 N 18.79 C 58.06 H 3.23 N 18.06 S 10.32 C 63.60 H 4.59 N 14.84 C 64.86 H 5.41 N 18.92 C 59.70 H 3.48 N 20.90 C 61.97 H 3.29 N 19.72 C 70.97 H 5.38 N 15.05 8.44 (AA9 2H) 8.00 (BB9 2H) 7.94 (AA9 2H) 7.80 (BB9 2H) 7.83 (BB9 2H) 7.08 (AA9 2H) 3.93 (OMe s 3H) 7.56 (BB9 2H) 6.80 (AA9 2H) 3.10 (NMe2 s 6H) 8.42 (AA9 4H) 8.00 (BB9 4H) 7.92 (AA9 4H) 7.80 (BB9 4H) 7.82 (BB9 4H) 7.08 (AA9 4H) 3.93 (OMe × 2 s 6H) time substitution is suppressed.There is a significant difference in the dissociating power of these two solvents (relative permittivities at 293 K are equal to 7.4 and 49 respectively). Experimental Preparation of dipotassium (disodium) 1,6-dinitro-COT Method 1. A filtered solution of freshly prepared dipotassium COT [from COT (1.04 g) and K (0.95 g)] in THF (40 ml) was added to a solution of 1,6-dinitro-COT (1.94 g 0.01 mol)9 in THF (20 ml) at 240 8C under argon. The reaction mixture was stirred at 240 8C for 30 min after which the temperature was raised to 25 8C. A yellow precipitate of 3 was formed and this was filtered off washed twice with cold THF and dried in vacuo over phosphorus pentoxide to yield a dry solid (2.6 g) (Found C 35.30; H 2.24; N 10.22; K 28.05.Calc. for C8H6K2N2O4 C 35.12; H 2.32; N 10.14; K 27.71%). The disodium derivative of 1,6-dinitro-COT was obtained in the same manner from disodium COT (Found C 40.22; H 2.31; N 11.53; Na 18.92. Calc. for C8H6N2Na2O4 C 40.00; H 2.50; N 11.67; Na 19.17%). Method 2. A solution of 1,4-dinitrocycloocta-2,5,7-triene 10 (1.96 g 0.01 mol) in THF (40 ml) was stirred with dry potassium methoxide (1.41 g 0.02 mol) at 220 8C for 20 min and then warmed to 25 8C over 30 min. Dipotassium 1,6- dinitro-COT was formed as a bright yellow precipitate which was treated as described above. The dry solid was obtained in 94% yield (2.55 g). The disodium analogue was prepared with sodium methoxide.The elemental composition and spectra of the (Na/K) derivatives obtained by methods 1 and 2 were identical. In method 2 1,4-dinitrocyclooctatriene used as a starting Table 3 Absorption bands in the electronic spectra of cyclooctatetraene azo compounds obtained according to Table 1 Azo compound R lmax/nm e × 104/l mol21 cm21 6a 6b 6c 6d 7a 7b 7c NO2 SCN OMe NMe2 NO2 SCN OMe 306 356 236 323 248 342 257 460 304 364 236 322 398 250 342 400 2.20 1.42 0.88 1.06 1.74 1.95 1.46 2.10 3.60 2.04 1.76 2.22 1.25 2.22 3.06 2.76 material was synthesized by nitration of COT with N2O4. The resultant compound was purified by procedures given in ref. 10 to give white crystals which were dried in vacuo (no more than 1 h). Interaction between the dipotassium or disodium derivative of 1,6- dinitro-COT and benzenediazonium tetrafluoroborates a typical procedure A dry tetrafluoroborate (0.01 mol) was slowly added to a suspension of the dipotassium derivative 3 (1.36 g) or disodium derivative 3 (1.20 g 0.05 mol) in THF or DME (40 ml).When DMSO was used as a solvent 10 ml were utilized to dissolve substrate 3 and 20 ml to dissolve the diazo salt. The reaction mixture was stirred over 30 min at 25 8C. Nitrogen was evolved in the course of the reaction and when this ceased the reaction Scheme 4 N2 + MeO N2 • MeO MeO OO• MeO OOH MeO + e OH MeO –N2 • +O2 +H• OH MeO +N2O4 –1/2 O2 NO2 –HNO2 8 750 J. Chem. Soc. Perkin Trans. 1 1997 mixture was stirred for a further 30 min and then filtered; a small quantity of this filtrate was examined by GLC (see below).The remaining filtrate was concentrated to 25% of its original volume. The resulting precipitate was collected and in solution subjected to chromatography (22 × 600 mm silica gel column; eluent hexane–ethyl acetate 3 1). The solid resulting from filtration of the reaction mixture was treated with cold acetone (3 × 10 ml) dried and analysed by means of IR spectroscopy and qualitative analytical methods. The salts MNO2 and MBF4 (M ]] Na K) were shown to be components of the solid although their yields were not determined. The yields of 1,6-dinitro-COT 1 its azo derivatives 6 and 7 nitrogen gas and benzenes RC6H5 are given in Table 1. Tables 2 and 3 show the analytical data upon which identification of the azo products 6 and 7 was established. Quantities of RC6H5 were determined by a GLC method with authentic standard materials introduced into the mixtures being analysed.Nitrogen was used as a carrier gas in all cases. For anisole and N,N-dimethylaniline a stainless-steel column (3 × 3700 mm) was used. The stationary phase was PEG-20M on silanized Chromatone N-AW 40–60 mesh. For phenyl thiocyanate and nitrobenzene a glass column (2 × 2000 mm) was employed. In this case the stationary phase was 5% SE-30 on silanized Chromatone N-AW-DMCS 20–25 mesh. 1H NMR Spectra were obtained on a Bruker WP-200 instrument using (CD3)2CO as a solvent with SiMe4 as a standard. Electronic absorption spectra were recorded using a Specord UV–VIS spectrometer and a cuvette of 1 cm diameter with MeOH as solvent and with 1023 mol l21 concentrations of the azo compounds. References 1 Z.V. Todres G. Ts. Hovsepyan in Abstracts of papers of the VI International Conference on Organic Synthesis August 10–15 1986 Moscow Russia. 2 Z. V. Todres J. Organomet. Chem. 1992 441 349. 3 Z. V. Todres S. P. Avagyan and D. N. Kursanov J. Organomet. Chem. 1975 97 139. 4 Z. V. Todres G. Ts. Hovsepyan V. I. Bakhmutov A. Yu. Kosnikov S. V. Lindeman and Yu. T. Struchkov Zh. Org. Khim. 1989 25 75 (in Russian) (Chem. Abstr. 1989 111 77532t). 5 G. J. Fray and R. G. Saxton The Chemistry of Cyclo-octatetraene and Its Derivatives Cambridge University Press London 1978 p. 48. 6 Z. V. Todres G. Ts. Hovsepyan I. A. Garbuzova I. V. Stankevich and V.
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