J. CHEM. SOC. PERKIN TRANS. I 1989 Reactivity of PhenyI iodonium Bis(a ry I -or a I kyI-suI phoriyI )methyIides towards Thiobenzophenones Lazaros Hatjiarapoglou and Anastassios Varvoglis * Laboratory of Organic Chemistry, University of Thessaloniki, Thessaloniki, 540 06, Greece Thermal reactions of several phenyliodonium bis(ary1- or alkyl-sulphony1)methylides with some thiobenzophenones are described. 4,4'-Dimethoxythiobenzophenone affords exclusively 2-arylsul- phonyl -3-(4-met hoxyphenyl) -6-met hoxybenzo [b]thiophenes, whereas other thiobenzophenones may give also gem- bis(arylsu1phonyl)thiiranes and in one case an unsaturated gem-disulphone. Some oxidation reactions of an ylide with various substrates occur either thermally or photochemically. Aryliodonium ylides are emerging as a reactive and versatile class of compounds, the chemistry of which has been recently summarised."2 The majority of iodonium ylides come from active methylene compounds, especially P-diketones, in which both hydrogen atoms have been replaced by the phenyliodonio (PhI+) group; the positive charge is internally compensated by a negative charge. One interesting property of phenyliodonium ylides is their ability to serve as carbene (or carbenoid) precur~ors,~*~whereas they may also react with electrophiles from their carbanionic C5 (or 0 in ylides with 0x0 and with nucleophiles from their cationic I.6 Recently the synthesis and some reactions of phenyliodonium bis(ary1- sulphonyl)methylides, (la),? notably with alkenes and alkynes have been reported from our laboratory.'*' We have ex-tended our studies on the reactivity of (la) using substrates with a C=S bond, i.e.thiobenzophenones. Analogous reactions give also some related bis(sulphony1) ylides. Results and Discussion The property of such well known carbene precursors as di- azo compounds and phenyl(trihalogenomethy1)mercury com-pounds lo to give thiiranes in their reaction with thioketones combined with the low reactivity of bis(phenylsulphony1)-diazomethane has led us to examine the reactivity of (la) towards thiobenzophenones. Phenyliodonium bis(phenylsu1- phony1)methylide (la) and several thiobenzophenones reacted in solution under a variety of conditions to give a complex mixture of products from which no pure compound could be isolated apart from the disulphone (PhSO,),CH,. However, when an intimate mixture of (la) and p,p'-dimethylthio- benzophenone (2a) in excess containing a catalytic amount of Cu(acac), was briefly heated without any solvent until it (3a) Scheme 1.t Named by IUPAC rules of nomenclature these would be phenyliodoniobis(arylsulphonyl)methanides. melted, it afforded 2,2-di-p-tolyl-3,3-bis(phenylsulphonyl)-thiirane (3a) in 27%yield (Scheme 1). With p,p'-dimethoxythiobenzophenone (2b) no thiirane was formed but instead 3-p-methoxyphenyl-6-methoxy-2-phenyl-sulphonylbenzo[b]thiophene, (4a), was obtained in 39% yield (Scheme 2). I (la-d) (2b-C) At (&a-f) Scheme 2. Two other thioketones, p-methoxythiobenzophenone and p-methoxy-p'-nitrothiobenzophenonewere oxidised by (la) to the corresponding benzophenones under various conditions, even in an inert atmosphere.In order to test the scope of the reaction further some other phenyliodonium bis(alky1- or aryl-sul-phony1)methylides (lM)reacted with the thioketone (2b) and also with p-methyl-p'-methoxythio benzophenone (2c) and found also to afford benzothiophenes, (4b-f) (see Table 1). All the benzo[b]thiophenes are new compounds and their structures have been established from analytical and spectro- scopic data (see Table 2). They are yellow, their most characteristic property being the yellow-greenish fluorescent colour in solution. Their electronic spectra are of diagnostic value since they show two intense absorptions in the region of 340 and 390 nm, with E values in the range of 10000.In contrast, the thiirane (3a) is colourless with a U.V. absorption at 320 nm. The i.r. spectra of (4) have the expected SO, absorptions at 1 305 and 1 160cm-I and in the 'H n.m.r. spectra 4-and 5-H of the benzothiophene ring appear often as a doublet at low field, near S 8;7-H has been identified only in (4f) and it resonates at high field, 6 6.82-6.95. The mass spectra of (4) always have a molecular ion of high intensity and a characteristic A4 -RSO, fragment ion. A further thiirane, (3b), has been obtained from the ylide (le) and thiobenzophenone (2c) (Scheme 3). No benzothiophene could be detected in this reaction, even by raising the temperature. The reaction of the ylide (Id) with thiobenzophenone (2c) gave besides the benzothiophene (4f) the unsaturated di-sulphone(5) in 20% yield (Scheme 4).3 80 J. CHEM. SOC. PERKIN TRANS. I 1989 Table 1. Benzo[b]thiophenes (4) from phenyliodonium bis(ary1 or alky1)sulphonyl methylides (1) and thiobenzophenones (2) Conditions Benzo[b]thiophene* Ylide Thio benzophenone ("C, min) (% yield) Ph+I -C(SO,Ph), (p-MeOC,H,),C=S 110,5 (4a) R=Ph, Ar=p-MeOC,H4 (la) (2b) (39)Ph+I-C(SO,Tol), (2b) 110, 5 (4b) R=Tol, Ar=p-MeOC,H, (Ib) (35)Ph'I -C(SO2C6H4Cl-p), 110, 10 (4c) R = p-ClC,H4, Ar = p-MeOC& (W (44) (14 120, 15 (4d) R = p-ClC,H,, Ar = TOI (42)Ph'I -C(SO,Me), 110,5 (4e) R = Me, Ar = p-MeOC& (14 (83) (14 loo, 10 (40 R = Me, Ar = To1 (48) * To1 is the p-tolyl group.Table 2. Properties of benzo[h]thiophenes (4) Found (%) Compound(Formula) M.p.a ("C) ~"(CDCl,) vma,.(NW) cm-' nm (log) r (Required) C H 7 (44 (4b) (4c) (C22H1 8°4s2) (C23H2004S2) 186-188 1761 76 186185 3.90 (s, 3 H), 3.97 (s, 3 H), 6.92-3.87 (s, 3 H), 3.92 (s, 3 H), 6.73-8.15 (m, 12 H) 2.35 (s, 3 H), 3.87 (s, 3 H), 3.95 (s, 3 H) 6.73-7.68 (m, 9 H), 8.00 (d, J9 Hz, 2 H) 1 305 1170 1 305 1 150 1 305 390 (4.05) 336 (3.89) 388 (3.92) 336 (3.81) 391 (4.09) 64.5 (64.37) 64.95 (65.07) 59.7 4.4 (4.42) 4.8 (4.75) 3.9 (C22H1 7C104s2) (4) (C22H1 7C103s2) (k)(C17H1604S2) (40(c17H 16°3s2) 179-1 165-1 157-1 8 1 67 59 7.65 (m, 9 H), 8.03 (d, J 9 Hz, 2 H) 2.47 (s, 3 H), 3.98 (s, 3 H), 6.83-7.83 (m, 9 H), 8.08 (d, J 9 Hz, 2 H) 3.22 (s, 3 H), 3.88 (s, 3 H), 3.92 (s, 3 H), 2.43 (s, 3 H), 3.25 (s, 3 H), 3.95 (s, 3 H), 6.82-6.95 (m, 1 H), 7.23-7.83 (m, 6 H) 6.9G7.75 (m, 7 H) 1155 1 305 1155 1 310 1165 1 305 1 155 336 (3.88) 386 (4.04) 334 (3.90) 376 (3.80) 331 (3.80) 378 (3.86) 328 (3.90) (59.39) 61.2 (61.60) 58.6 (58.60) 61.65 (61.42) (3.85) 4.0 (3.99) 4.5 (4.63) 4.8 (4.85) Recrystallisation from chloroform-hexane.Absorption maxima above 300 nm only cited. occur thermally with catalysis by C~(acac),.~*~ Alternative mechanisms involving zwitterionic intermediates which might result from interactions of intact ylides and thiones, e.g. (6) or (7), appear less likely, because the ylides decompose at the melting temperature of the mixture.+ + Scheme 3. Ar2C-C(S02R)2 IPh Ar2C=S--I-C(S02R)2 I II S-Ph With the exception of (3a) and (3b), thiiranes under the reaction conditions (1 10-120 "C) do not survive, being transformed into the benzothiophenes (4); in one case the alkene (5) was also isolated. The fact that p,p'-dimethyl-thiobenzophenone gave no benzothiophene suggests that the benzothiophenes (4d) and (4f) formed from p-methy1-p'-methoxythiobenzophenone are 3-p-tolyl and 6-methoxy substi- Scheme 4. tuted. The transformation of thiiranes to benzothiophenes requires expulsion of a sulphinic acid, reactivity previously There is little doubt that all the reactions between iodonium observed in reactions of the ylides (1) with alkenes and alkynes, ylides and thiobenzophenones involve the initial formation of a where indanic and indenic monosulphones were the main thiirane, in a formal cycloaddition of a bis(ary1 or alky1)sulphonyl products.8 It appears that the otherwise 'extremely difficult' carbene to the C=S bond, which may also proceed through a elimination of a sulphinic acid from a sulphone is effected easily thiocarbonyl ylide, since an equilibrium is possible between in gem-disulphones. thiiranes and thiocarbonyl ylides.Thermal dissociation of Thermal transformations of 2,2-diphenylthiiranes bearing a various iodonium ylides to carbenes has been demonstrated to good leaving group such as (8) into benzo[h]thiophenes (9) J. CHEM. SOC. PERKIN TRANS. I 1989 Table 3. Oxidations by (la) Substrate [ratio of (la): substrate] Ph,C(OH)C(OH)Ph, (1: 1) 1,2-Epoxycyclohexane(1:5.5) 1,2-Diphenyloxirane(1:2.5) Xylene-4,5-diamine (1 : 1) Ph,C=CPh, (1 : 1) PhCH=CH, (1 :excess) Ph,C=CH, (1:excess) PhCrCPh (I :5.5) 1,3-Benzodioxole (1 :8) Conditions R.t., 12 h R.t., 24 h R.t., 12 h R.t., 12 h R.t., 12 h hv, 75 min hv, 5 h hv, 5 h N,, hv, 5 min 381 Products (% yield") Ph,CO (98) 2-Hydroxycyclohexanone (59) PhCHO (41) + Ph,CHCHO (55) 1,1'-Azo-2-amino-4,5-dimethylbenzene(30) Ph,CO (6)b PhCHO (68)' Ph,CO (81) PhCOCOPh (30)b Pyrocatechol (75) Yields of isolated products (except for PhCHO and Ph,CHCHO), based on (la).Other products were also produced.8 have been reported.10,'4-17 These reactions are intramolecular aromatic electrophilic substitutions and Seyferth lo suggested that the thiirane may react through a ring-opened intermediate of type A or B, both of which are subsequently converted into the reactive species C, which eventually cyclises to (9) (Scheme 5)-(8) Br I + I[Ph2C--C=S I X or IPhZC=C-SBr IPh*C-C-=S X Br-I A 9 C Ph (9) Scheme 5.The reluctance of the spirothiirane (3b) to undergo the reaction to benzothiophene lends support to Seyferth's inter- mediate A, because a migration of the SO, group to C in (3b) would not be favoured. Among alternative mechanisms, a possi- bility involves direct attack from the aromaticp-methoxyphenyl ring at sulphur of the thiirane, with the intermediate formation of a benzothiete.Whatever the exact mechanism, it appears that strong activation is necessary for the ring closure and one phenyl group of the thiobenzophenone must bear a methoxy group. The reactions of p-methyl-p'-methoxythiobenzophenone (2c) gave, exclusively, 6-methoxy-3-(p-tolyl)benzothiophenes, in accordance with the better electron-donating character of the methoxy group as compared to the methyl group, although by necessity it is carbon from the mela position which attacks the electrophilic centre. With p,p'-dimet h ylthio benzophenone the activation is not sufficient, so that its reaction with (la) stops at the thiirane. A reaction of the mixed ylide PhIf-C-(SO,Tol)(SO,Me) with thiobenzophenone (2b) resulted in the isolation of only one benzothiophene, (4b), having a 2-p-tolylsulphonyl group, in 5% yield.This selectivity may be related to the higher electro- negativity of the MeSO, group in comparison to that of the TolSO, group (3.1 and 2.9 in Pauling's scale, respectively 18), so that MeSO, constitutes a better leaving group. The low yield of (4b) in this reaction is attributed to the low melting point of the ylide (90 "C)which is lower than the m.p. of (2b) (110 "C), so that extensive decomposition of the ylide took place before the melt was formed. Formation of the alkene (5) must be the result of thermal desulphurisation of its thiirane precursor. Such transformations are well known l9 and it may be expected that iodonium ylides which cannot be transformed eventually into benzothiophenes in their reaction with thiobenzophenones would give either thiiranes or alkenes (or both) depending on the reaction conditions. A by-product in all these reactions is benzophenone coming from oxidation of the thiobenzophenone.This side reaction becomes important when the thiobenzophenone bears electron- withdrawing substituents. It is not known how this oxidation is effected but it seems appropriate at this point to examine briefly the oxidative properties of (la), some of which have already been mentioned.' The ability of (la) to effect oxidations has been demonstrated to occur either thermally or photochemic- ally. Thermal oxidations were actually performed without heating and in the absence of catalyst.Photochemical oxi- dations, with one exception, were performed in the presence of air. The results of these reactions have been collected in Table 3. It is noted that several arylalkenes and diarylacetylenes, in addition to products derived from cycloaddition of bis(pheny1-sulphony1)methylene to the multiple bond, give also with (la) oxidation products, both thermally or photochemically.8 These exploratory experiments show the potential of (la) in effecting dehydrogenations, oxygenations, and cleavage of C-C or C-0 bonds of various types. The diversity observed can hardly be accounted for by a common route. Since in de- hydrogenations, either thermal or photochemical, bis(pheny1- sulphony1)methane was always a major product, the possibility of carbene formation' is ruled out; we suggest that a homolytic pathway is available here.The other types of oxidation are more involved and only in some of them was bis(phenylsulphony1)- methane formed. It seems that in addition to homolytic pathways, (la) can also transfer in some way one of its oxygen atoms to the substrate. The fate of the carbanionic moiety of (la) in these cases is not presently known. Despite the lack of more information about these oxidations, some of them might be used to advantage, especially the conversion of 1,3-benzodioxole into pyrocatechol. The latter was obtained in good yield, surpassing an analogous oxidative removal of the methylene group by lead tetra-acetate.,' Experimenta1 U.V.spectra were recorded with a Shimatzu 210A spectro- photometer, i.r. spectra (in Nujol) with a Perkin-Elmer 257 spectrometer, and 'H n.m.r. spectra on a Varian A-60A 382 instrument. Mass spectra were obtained from a Hitachi-Perkin- Elmer RMU-6L single focussing mass spectrometer at 70 eV. Starting Materials.-Thiobenzophenones and disulphones were known compounds. The preparation of the ylides (la-) has been described previously.' The iodonium ylides (Id-) have been obtained as follows. A cold solution of KOH (1.16 g, 20.7 mmoles) in MeOH (10 ml) was added to a stirred suspension of (MeSO,),CH, (1g, 5.8 mmol) in MeOH (10 ml) at -10 "C. The mixture was stirred at -10 "C for 60 min after which a solution of PhI(OAc), (1.87 g, 5.8 mmol) in MeOH (10 ml) was added gradually to it, the temperature being kept at -5 "C; stirring was then continued for 60 min.The reaction mixture was then set aside at -10 "C for 12 h after which the precipitate was collected, washed with cold MeOH, and dried in uuc'uo, to afford phenyliodonium bis(methylsu1phonyl)methylide (75%), m.p. 109--110°C; v,,,. 1295 and 1 115 cm-'; 6,-(CD,SOCD,) 3.02 (s, 6 H), 7.50-7.72 (m, 3 H), and 7.87-8.17 (m, 2 H); m/z 374 (M', 0.1%) (Found: C, 28.6; H, 3.0. C9H11104S2 requires C, 28.89; H, 2.96). Using the disuiphone of 173-dithiane under similar conditions 2-phenyliodonium- 1,3-dithian-2-ide 1,1,3,3-tetraoxide (le) was obtained (92%), m.p. 112-1 15 "C; v,,,. 1 300, 1 270, and 1 110 cm-'; 6H(CD,SOCD,) 2.02-2.45 (m, 2 H), 2.73-3.07 (m, 2 H), 3.2G3.67 (m,2 H), 7.45-7.72 (m, 3 H), and 7.83-8.17 (m, 2 H); m/z no M', 204 (C,H,I, 95%), and 184 (28).This ylide was insufficiently stable to provide a satisfactory elemental analysis. Reactions of Iodonium Ylides (1) with Thiobenzophenones: General Procedure.-An intimate mixture of the ylide (1-2 mmol) with thiobenzophenone (4-5 mmol) containing Cu- (acac), (1 mg) was heated under nitrogen in an oil-bath for a few minutes at 110 "C (for details see Table 1). The reaction mixture was dissolved in chloroform and passed through a silica gel chromatographic column (eluant chloroform or methylene dichloride-light petroleum) and after phenyl iodide and un- changed thiobenzophenone the 2-aryl- (or methy1)sulphonyl-3- aryl-6-methoxybenzo[bJthiophenesof Table 1 were obtained; their properties appear in Table 2.Under similar conditions the thiiranes (3a, b) and the alkene (5) were obtained. 3,3-Bis(phenylsufphonyf)-2,2-di-p-tolylthiirane(3a), This com- pound was obtained after heating (la) and (2a) at 120 "C for 20 min. Some p,p'-dimethylbenzophenone was also eluted before (3a), which was obtained in 27% yield as white crystals, m.p. 251-253 "C (from chloroform-hexane); vmaX. 1 325 and 1 160 cm-'; h,,,.(EtOH) 320 nm (log E 4.24); GH(CDC1,) 2.35 (s, 6 H) and 6.82-8.00 (m, 18 H); m/z488 (M -32) (Found: C, 64.7; H, 4.8. C,,H,,O,S, requires C, 64.59; H, 4.65). 2,2- Bis(p-methoxypheny1)- 1,4,8-trithiaspiro[2.5]octane 4,4,8,8-tetraoxide (3b).This compound was obtained after heating (le) and (2c) at 110°C for 5 min. Some p,p'- dimethoxybenzophenone was eluted before (3b); it was obtained as white crystals (26%), m.p. 245-247 "C (from ethyl acetate- hexane); v,,,. 1 325 and 1 135 cm-'; G,(CDCl,) 2.47 (t, J7 Hz, 2 H),3.55(t, J7Hz,4H),3.83(s,6H),6.85(d,J9Hz74H),7.3O(d, J 9 Hz, 4 H); m/z 408 (M -32) (Found: C, 51.8; H, 4.7. C,,H,,06S3 requires C, 51.80; H, 4.58). 1,l-Bis(methylsulphonyl)-2-(p-methylphenyl)-2-(p-metho~y-pheny1)ethylene (5). This compound was obtained from the reaction of (Id) with (2c) (Table 1). It was eluted after (40 as white crystals (2073, m.p. 260-262 "C (from ethyl acetate- hexane); v,,,, 1 600,l 310, and 1 130 cm-'; v,,,.(EtOH) 330 nm (log E 4.03); FH(CDC1,) 2.42 (s, 3 H), 3.38 (s, 3 H), 3.42 (s, 3 H), 3.87 (s, 3 H), and 6.96-7.33 (m, 8 H); m/z 380 (M') (Found: C, 57.1; H, 5.4.C,,H2,0,S2 requires C, 56.82; H, 5.30). J. CHEM.SOC. PERKIN TRANS. I 1989 Oxidations.-Reaction conditions are given in Table 3. All thermal reactions were performed in methylene dichloride. The photochemical reactions were performed by irradiating the samples (in 10 ml of acetonitrile) in a Pyrex tube with a Philips 400 W low-pressure lamp. After removal of the solvent and volatiles, residues were subjected to column chromatography (using silica gel and either ethyl acetate-light petroleum or methylene dichloride-light petroleum). Phenyl iodide was always the first to be eluted. Oxidation of 4,5-dimethylphenylenediamine. The oxidation product, trans-2,2'-diamino-4,4',5,5'-tetramethylazobenzene, was obtained as red crystals, m.p.208-210°C (from chloro- form-hexane); v,,,. 3 440 cm-l; m/z 268 (M +,45%) (Found: C, 71.2; H, 7.4; N, 20.85. C,,H2,N4 requires C, 71.61; H, 7.51; N, 20.88). Oxidation of cyclohexene oxide. 2-Hydroxycyclohexanone was obtained, m.p. 108-1 11 "C (lit.,2' m.p. 11 3 "C). Oxidation of trans-l,2-diphenyloxirane.An inseparable mix- ture of benzaldehyde and diphenylacetaldehyde was identified; the ratio of compounds was determined by 'H n.m.r. spectro- scopy, using authentic samples as standards. Oxidation of 173-benzodioxole. Pyrocatechol was obtained, m.p. 104-106 "C, identical with an authentic sample. Acknowledgements We thank the L.Zervas Foundation for a scholarship (to L. H.) and the Royal Society of Chemistry for financial assistance (to A. V.). References 1 G. F. Koser, in 'The Chemistry of Functional Groups,' Supplement D, Wiley, New York, 1983, ch. 18, pp. 774-806. 2 A. Varvoglis, Synthesi.y, 1984, 709. 3 Y. Hayashi, T. Okada, and M. Kawanisi, Bull. Chem. SOC.Jpn., 1970, 43, 2506. 4 J. N. C. Hood, D. Lloyd, W. A. MacDonald, and T. M. Shepherd, Tetrahedron, 1982, 38, 3355. 5 W. Hanefeld and B. Spangenberg, Arch. Pharm. (Weinheim), 1987, 320, 666. 6 S. Spyroudis, Liebigs Ann. Chem., 1986, 947. 7 L. Hatjiarapoglou, S. Spyroudis, and A. Varvoglis, J. Am. Chem. SOC.,1985, 107, 7178. 8 L. Hatjiarapoglou, A. Varvoglis, N. W. Alcock, and G. Pike, J.Chem. SOC.,Perkin Truns. I, 1988, 2839. 9 M. D. Bachi, 0. Goldberg, A. Gross, and J. Vaya, J. Org. Chem., 1980,45, 1481. 10 D. Seyferth, W. Tronich, R. S. Marmor, and W. E. Smith, J. Org. Chem., 1972, 37, 1537. 11 J. Dieckman, J. Org. Chem., 1965, 30, 2272. 12 K. Oka, A. Dobashi, and S. Hara, J.Am. Chem. Soc., 1981,103,2757. 13 P. D. Magnus, Tetrahedron, 1977, 33, 2019. 14 A. Schonberg and L. Vargha, Chem. Ber., 1931,64, 1390. 15 H. Staudinger and J. Siegwart, Helv. Chim. Acta, 1920, 3, 840. 16 A. Schonberg and L. Vargha, Liebigs Ann. Chem., 1930,483, 176. 17 G. L'abbC, J. P. Dekerk, C. Martens, and S. Toppet, J. Org. Chem., 1980,45,4366. 18 J. E. Huheey, J. Phys. Chem., 1966, 70, 2086. 19 D. C. Dittmer, in 'Comprehensive Heterocyclic Chemistry,' Pergamon Press, 1984, vol. 7, p. 140. 20 Y. Ikeya, H. Taguchi, and I. Yiosioka, Chem. Phurm. Bull., 1979,27, 2536. 21 R. Willstatter and E. Sonnenfeld, Chem. Ber., 1913, 46, 2952. Received 23rd February 1988; Paper 8/00715B
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