Pyrylium salts. Part V. 5,6,12,13-Tetrahydro-5,13 : 6,12-bisepithiodibenzoa,fcyclodecene-7,14-diones by dimerisation of 2-benzothiopyrylium-4-olate

摘要

13 66 J.C.S. Perkin IPyrylium Salts. Part V.l 5,6,12,13-Tetrahydro-5,13 : 6,12-bisepithiodi-benzo a, f cyclodecene -7,14-d iones by D i rner isat io n of 2- Benzot h iopyry I -ium-4-olateBy Kjell Undheim * and Sigurd Baklien, Department of Chemistry, University of Oslo, Oslo 3, Norway2 - Be nzot h i o pyr y I i u m - 4- o la te, s y n t h esised fro m i sot h i o c h ro ma n - 4 - one a nd i so I at ed as the perch 1 or i c acidsalt, is readily dimerised to give stereoisomeric 5.1 3 :6,12-bisepithiodibenzoa,f cyclodecenes ; the syn-isomeris the major product. Spectroscopic data for both isomers and X-ray data for the syn-form are discussed.THREE-MEMBERED rings containing one heteroatomreact with 1,3-dipolarophiles through an ylide inter-mediate.2.3 When such a three-membered ring is fusedonto another ring of medium size, thermal conrotatoryring opening is not permitted by the geometry of thesystem, whereas disrotatory photochemical opening isa l l o ~ e d .~ In fused indeno-systems, however, both theformally disallowed and the allowed opening of thethree-membered ring occur, as shown by 1,3-dipolar1 Part IV, K. Undheim and B. P. Nilsen, Acta Chem. Scand., B,in the press.J. H. Hall and R. Huisgen, Chem. Comnz., 1971, 1187.3 H. Hamberger and R. Huisgen, Chem. Comm., 1971, 1190.J. W. Lown and K. Matsumoto, J . Org. Chem., 1971, 36,J. W. Lown and K. Matsumoto, Canad. J . Chem., 1971,1405.49, 3446.addition reaction^.^-^ In the absence of a suitabledipolarophile, dimerisation may take The firstisomerisation reactions of this type were reported forphenyl-substituted indanone epoxides : 'y9 these (1 ;X = 0) are valence isomers of 2-benzopyrylium-4-olate (3; X = 0).The 2,3-diphenyl epoxide (1; X =0) exists in an equilibrium with the mesoionic system(3); the equilibrium position is much in favour of theepoxide i s ~ m e r . ~ ? ~ Presumably the reactive carbo nyl654.86, 3814.1964, 1847.1966, $8, 4942,6 D. L. Garling and N. H. Cromwell, J . Org. Chem., 1973, 38,7 E. F. Ullman and J. E. Milks, J . Amer. Chem. Soc., 1964,8 H. E. Zimmerman and R. D. Simkin, Tetrahedron Letters,@ E. F. Ullman and W. A. Henderson, J . Amer. Chem. Soc.1975 1367ylide (2) may arise from either of these forms. Therelated isomerisation of isoquinolinium-4-olates (3 ; X =NR) to la,6a-dihydroindeno1,2-bazirin-6(1H)-ones (1 ;X = NR) does not appear to have been reported;isomerisation in the opposite direction, however, con-stitutes a ready synthesis of isoquinolinium-4-olates.10The azomethine ylide structure (2) explains the 1,3-dipolar character demonstrated by cycloadditions of N-methylisoquinolinium-4-olate ; u 1,3-dipolar characterhas also been demonstrated for pyridinium-3-01ates.l~Pyrylium-3-olate and its thio-analogue, however, havenot been available for such studies.0( 2 )SCHEME 10-( 3 )The simple pyrylium- and thiopyrylium-3-olates areexpected to be unstable, as reflected in the low stabilitiesof the pyrylium and thiopyrylium cations.13 Wedescribe here a study of 2-benzothiopyrylium-4-olate(6). Synthesis of this compound from i t s valenceisomeric episulphide (1; X = S) by analogy to thephotolytic isomerisation of the aza-analogues to theisoquinolinium-4-olates lo was not attempted in view ofthe instability of activated episulphides ; the synthesiswas in fact carried out according to Scheme 2.0-0 OH( 4 )t( 7 1SCHEME 2(Benzy1thio)acetic acid (4) was cyclised to isothio-chroman-4-one (5) by means of phosphorus pent0~ide.l~Pyryliuiii cations are readily generated from 4H-pyransthrough hydride abstraction by triphenylmethyl per-chlorate; l5 the trityl reagent was also successful in thepresent case and 2-benzothiopyrylium-4-olate, as itsperchloric acid salt, could be recrystallised from aceticacid. Preparation in the presence of acetic anhydrideand acetic acid gave the 4-acetoxythiopyrylium cation(7) in excellent yield.The acetoxy-derivative (7) insolution in trifluoroacetic acid (TFA) was completelydeacetylated after a few hours at room temperature, andthe mesoionic compound (6) was again obtained as theperchloric acid salt. The n.m.r. spectra of the thio-pyrylium salts in CD,CN are characterised by low fieldabsorptions, especially for H-1 which resonates as adoublet at 7 -0.5 for (6) and at -0.9 for the acetate (7) ;in isoquinolinium analogues examined the chemicalshift for H-1 is in the range 7 0.4-1.1.10316The thiopyrylium salt (6) is readily attacked by waterand is thus less aromatically stabilised than its aza-analogues.Addition of triethylamine to a solution of theperchloric acid salt of (6) in acetonitrile and tetrahydro-furan resulted in a deeper yellowish-green colouring ;the colour had faded after a few min. The colouring wassustained for a longer period at -60 "C, but the samereaction took place as discussed below. Addition of theperchloric acid salt of (6) to a solution of potassium t-butoxide gave the same major product but the totalproduct was more heterogeneous. U.V. absorptionsrecorded during the addition of triethylamine showedthe disappearance of the long-wave 390 nm band of theperchloric acid salt (6) with the transient appearance oftwo new bands at 355 and 436 nm; A,,,. for the finallong-wave band was ca. 365 nm.The final spectrum wasrelated to that of isothiochroman-4-one recorded inacetunitrile. The first shift in the U.V. maxima isattributed to the phenol-phenolate shift due to gener-ation of the mesoionic system (6). The final product wascomposed of two substances without salt-like charac-teristics. These were separated by column chromato-graphy on silica gel; both showed a molecular ion atm/e 324 and had related mass spectral fragmentationpatterns, this implied that dimerisation of the thiopyry-liumolate (6) had occurred. The isomer ratio was 1 : 7.The same product was obtained in attempted cyclo-addition reactions with the usual 1,3-dipolarophilesduring addition of the triethylamine ; no cycloadductswere formed. Dimerisation in the analogous isoquino-linium series has not been reported.The equilibriummixture of I ,3-diphenyl-2-benzopyrylium-4-olate (3 ;X = 0) and its epoxide (1) , however, is readily dimerisedin such a way that the carbonyl group in one epoxidemolecule (1) adds as a 1,3-dipolarophile to the carbonylylide (2) .7 Spectroscopic data exclude such a dimeris-ation in the present case. Photolysis of the 2-methyl-3-phenyl epoxide (1) has yielded 6 of a dimeric material.The structure suggested from spectroscopic evidenceis analogous to structure (9) described below for thethiopyrylium dimer; no further stereochemistry wasdiscussed. The spectroscopic data for the thiopyryliumdimers suggest that both have the same carbon skeleton.They both have a strong carbonyl absorption band atlo I?.E. Hansen and K. Undheim, J.C.S. Perkin I, 1975, 305.l1 N. Denis, A. R. Katritzky, and Y. Takeuchi, J.C.S. Perkin I,l2 A. R. Katritzky and 3'. Takeuchi, J . Chem. Soc. ( C ) , 1971,l3 J. Degani, R. Fochi, and C. Vincenzi, Boll. sci. Fac. Claim.14 C. C . Price, M. Hori, T. Parasaran, and M. Polk, J . Amer.l6 K. Undheim and E. T. IZlstensen, A d a Chem. Scaszd., 1973,l6 K. Undheim and P. E. Hansen, Chemica Scripta, 1973, 3,1972, 2054.s74. 27, 1385.i d Bologna, 1965, 23, 21.Chem. SOL, 1963, 85, 2278.1131368 J.C.S. Perkin I1670 cm-l (KBr). The major isomer has U.V. bands(MeCN) at 292 and 371 nm and the minor isomer bandsat 298, 350, and 365 nm. The n.m.r. spectra containsignals for two coupled methine protons besides thearomatic protons.The data are consistent with face-to-face dimerisation. A double-layer transition state inwhich the carbonyl groups lie above each other on thesame side is unlikely because of directional polarisationin the monomers which results in dipolar or electrostaticrepulsion. With the carbonyl groups arranged onopposite sides, however, attractive forces exist betweenthe charge centres; the syn- (a) and the anti- (b) arrange-ments lead to the respective dimers shown (Scheme 3).0 3: 0constant is 12 Hz. The methine protons show furthersecondary coupling (2 Hz). When syn-(9) is dissolved in2H6dimethyl sulphoxide and dilute sodium deuteriumoxide is added, the protons next to the carbonyl groupsare rapidly exchanged ; the benzyl methine protons arealso easily exchanged.After exchange of the twoprotons next to the carbonyl groups (H-6 and -13) thesinglet due to remaining two benzyl protons appearedbroad, presumably because of long-range aromaticcouplings. The secondary splitting of 2 Hz disappearedon deuteriation and is therefore ascribed to couplingbetween the methine protons on either side of the sulphurbridge. A secondary coupling of about 2 Hz is also seen0( b )SCHEME 30anti-( 9 1From the n.m.r. spectra (see later) the major isomerwas assigned the syn-structure, and this was confirmed byX-ray analysis.l7 The molecule has a two-fold axis ofsymmetry. The faces are planar within 0.1 with thesulphur atom 1 A out of the plane. The planes aretilted; the internal angle is 113" between the planes andthe plane through the carbon atoms of the dithian ring.The distance between a carbonyl carbon (C-7) and theclosest non-bonded aromatic carbon atom (C-4a) is2.763 A.The shortest interplanar distance betweenaromatic carbon atoms (C4a and -1la) is 3.242 A; thenormal stacking distance for aromatic rings is 3.40 A incrystals.18 In syn-(9) the benzene rings are displacedsideways relative to one another, which brings the x-electrons of the carbonyl groups near to the x-electrons ofthe benzene rings. The short interplanar distanceimplies repulsion between the x-systems ; this is reflectedin the C(5)-C(6) and C(12)-C(13) bond lengths (1.577 A),which are significantly longer than the normal carbon-carbon single bond; the carbon-sulphur bonds, however,have normal values (1.811 and 1.815 A).17 The sulphuratoms can be regarded as part of a 1,4-dithian ring lockedin the boat conformation.Accordingly the torsionangle between the vicinal protons is small; the experi-mental value is 10.7 amp; 30,17 and the vicinal couplingin the spectrum of the anti-isomer, which is rigidly lockedin a chair conformation of the 1,4-dithian ring; thevicinal coupling constant of the methine protons was 5.5Hz. In both isomers the methine protons on either sideof the sulphur atom are nearly synperiplanar ; this maybe the reason for the magnitude of the observed coupling.The resonances for the aromatic protons in the syn-isomer occur at higher field (z 2.6-3.1) than in the anti-isomer (7 1.8-2.7).The aromatic protons in isothio-chroman-4-one (5) resonate in the region "c 2.0-2.8.The major shift difference occurs in the case of thearomatic proton ortho to the carbonyl group, which isresponsible for the lowest-field aromatic signal in anti-(9) and (5). In the syn-isomer this proton lies above abenzene ring and is thus in the aromatic shielding zonewhich effectively counteracts the anisotropy effect f romthe carbonyl group.The mass spectra of the dimers contain the same majorfragments but differ in relative intensities. The basepeak is at m/e 134 (c8H6s) and the relative intensities ofthe molecular ion are 15 and 30 for the syn- and anti-isomer, respectively. The spectrum from the perchloric17 P.Groth, Acta Chem. Scand., A , in the press.l* D. J. Cram and J. M. Cram, Accounts Chenz. Res., 1971,4, 2041975 1369acid salt of the thiopyryliumolate (6) shows dominatingpyrolytic dimerisation before evaporation and thespectrum resembles that of the anti-isomer in relativefragment intensities. Direct evaporation of the species(6) appears to be insignificant. This observationillustrates the difference in stabilisation by sulphur andnitrogen atoms of cationic aromatic systems : simpleisoquinolinium-4-olates and pyridinium-3-olates arereadily evaporated in the mass spectrometer withoutisomerisation.1Q~ 2OThe benzene rings in the dirner (9) are planar, not bentas in many highly strained cyclophane systems.15 Thestructure is rigid because of the sulphur cross-bondingpreventing isomer interconversion ; the anti-isomer isprobably for steric reasons thermodynamically the morestable. The syn-isomer bears some resemblance to thesymmetrical sandwich-like 2,2orthocyclophane formedby intramolecular photodimerisation of 1,3-bis-( a-naphthy1)propane; 21 the isomer formed is the one whichhas maximum overlap of the x-orbitals in the transitionstate.21 Preferential endo-adduct formation in 1,3-dipolar cycloadditions and in Diels-Alder reactions hasbeen interpreted in terms of secondary orbital overlapin the transition state.6 Similar arguments may beadvanced for the preferential formation of the syn-isomer of (9), although the dimerisation may be a two-step process via an intermediate zwitterion-like structure(8).Another possibility also exists for stereochemicaldirection in the dimerisation of (6) : differential polaris-ation in the benzene rings, which is likely because of thecharge separation in the hetero-rings, may result inweak dipolar attraction between the benzene rings whenarranged as in (a). The stereochemistry of the finalproduct is already determined by the first carbon-carbon bond formation in the absence of epimerisation.That the dimerisation reaction is fast and selective isshown by the failure of concerted 1,3-dipolar cyclo-additions with all the dipolarophiles tried.EXPERIMENTAL3I.m.r. spectra were recorded on a Varian A-60 A orA-100 instrument, U.V. spectra on a Cary 14 spectrophoto-meter, and mass spectra on an A.E.1.-902 spectrometer.Isothiochroman-4-one (5), prepared as described,14 hadand 2.3-2.8 (3H, aromatic) ; A,, (MeCN) 248 (log E 3.99),291 (3.23), and 344nm (2.36); m/e 164 (63, M+), 118 (loo),90 (59), and 89 (17).4-Hydroxy-2-benzothiopyrylium Perchlorate (6) .-(a) Iso-thiochroman-4-one (3.28 g, 0.020 mol) was dissolved inanhydrous acetonitrile (20 ml) and triphenylmethyl per-chlorate 22 (6.50 g, 0.019 mol) was added.The reactionmixture was heated at 55-60 "C for 10 min. The cold'F (CD,),SO 6.4 (2 x H-3), 6.0 (2 x H-1), 2.0-2.2 (H-5),precipitated greenish perchlorate collected. After washingwith anhydrous ether and methylene chloride the materialwas recrystallised from acetic acid; yield 4.00 g (80),m.p.175-176' (decomp.) (Found: C, 41.3; H, 2.8.C,H,OS,HClO,requires C, 41.15; H, 2.7) ; 7(CD,CN) 1.2-1.9 (4H, aromatic and H-3) and -0.5 (H-1, d, J 3 Hz);A,, (MeCN) 230 (log t 4.23), 258 (4.51), 310 (3.68), 319(3.60), and 390 nm (3.74); mle 324 (33, -If+), 291 (34),162 (go), 149 (13), 147 (14), and 134 (100).(b) 4-Acetoxy-2-benzothiopyrylium perchlorate (3.04 g,0.01 mol) was dissolved in trifluoroacetic acid (50 ml) andleft a t room temperature for 5 h. The solution was thenevaporated at reduced pressure and the residue (6) recrystal-lised from acetic acid; yield 1.83 g (70).4--4 cetoxy-2-benzothiopyryliurtz Perchlorate (7) .-Isothio-chroman-Cone (1.64 g, 0.01 mol) was dissolved in acetic acid(10 ml) and acetic anhydride (10 ml), and triphenylmethylperchlorate (3.42 g, 0.01 mol) was added.The mixture washeated at 60-70 OC for 5-10 min. The progress of thereaction was indicated by the dissolution of the perchlorateand the green colour of the resultant solution. The coldsolution was poured into anhydrous ether (250 ml) and theprecipitated salt washed with ether and methylene chloridebefore recrystallisation from acetic acid-acetonitrile ; yield2.50 g (95), m.p. 150' (decomp.) (Found: C, 43.6; H,3.25. C,,H,O,S,HClO, requires C, 43.35; H, 2.95) ;7 (CD,CN) 7.4 (Ac), 1.2-1.9 (4H, aromatic), 0.8 (d, Jr,3 3Hz, H-3), and -0.9br (d, H-1); A,, (MeCN) 230 (log E4.23), 258 (4.51), 310 (3.68 ),319 (3.60), and 390 nm (3.74).syn- and anti-5,6,12,13-Tetral~ydro-5,13: 6,12-bisepithio-dibenzoa,fcyclodecene-7,14-dione (9) .-4-Hydroxy-2-benzo-thiopyrylium perchlorate (2.62 g, 0.01 mol) was dissolved inanhydrous tetrahydrofuran (150 ml) and acetonitrile (50 ml) .Triethylamine (1.01 g, 0.01 mol) in tetrahydrofuran (50 nil)was added dropwise with stirring over 1 h to the solution atroom temperature.A deeper yellowish-green colour ap-peared during the addition and disappeared rapidly after-wards. The solution was then washed with water, dried,and evaporated. The residue was dissolved in methylenechloride and chromatographed on silica gel (0.2-0.5 mm).The syn-dimer (major isomer) was eluted with methylenechloride after the anti-dimer; yield 1.19 g (74), m.p. 335"(subl.) (from chloroform) (Found: C, 66.55; H, 3.85.C,,H,,0,S2 requires C, 66.65; H, 3.7); 7 (CD,),SOJ 5.65.0br (9, H-5 and -12), and 3.6-3.1 (8H, aromatic); lb,(MeCN) 221 (log E 4.27), 241 (4.28), 292 (3.59), and 371 nm(2.77); m/e 324 (15, M+) 291 (22), 162 (46), 149 (83), 147(lo), and 134 (100).The yield of the anti-isomer was 0.16 g (10) ; m.p. 242-243 "C (from chloroform) (Found: C, 66.4; H, 3.9).Hz, H-6 and -13), 5.5br (4, H-5 and -12), 1.8-2.0 (2H,aromatic ortho t o CO), and 2.3-2.7 (6H, aromatic); Amax.(MeCN) 246 (log t 4.34), 298 (3.80), 350 (2.94), and 365 nm(2.95); mje 324 (32, M+), 291 (43), 162 (94), 149 (14), 147(19), and 134 (100).(9, J5,6 = J12.13 = 12, J5.13 = J f j , l Z = Hz, H-6 and -13)If (CD3)2Sol 6*3 (9, J S , 6 = Jl2.13 = 5*5, J5.13 = J6.12 =solution was poured into anhydrous ether (250 ml) and the 4/2709 Received, 30th December, 19741T. Gr~rnneberg and K. Undheim, Ovg. Mass Spectvometly, 21 E. A. Chandross and C. J. Dempster, J . Amel,. Chem. Soc.,1972, 6, 226. 1970. 92. 703.2o P. E. Hansen and K. Undheim, Acta Chem. Scald., 11, 1975, 22 'H:-J. Dauben, L. R. Honnen, and K. M. Harmon, J . Org.29, 221. Clzem., 1960, 25, 1442