Keten dithioacetals. Part 22. Reaction of polarised ketoketen dithioacetals with dimethyl acetylenedicarboxylate

摘要

J. CHEM. SOC. PERKIN TRANS. I 1983 Keten Dithioacetals. Part 22.' Reaction of Polarised Ketoketen Dithioacetals with Dimethyl Acetylenedicarboxylate Jai N. Vishwakarma, Hiriyakkanavar Ha,* and Hiriyakkanavar Junjappa Department of Chemistry, North- Eastern Hill University, Shillong 793003, Meghala ya, India Ketoketen dithioacetals (1a-e) react with dimethyl acetylenedicarboxylate (2) to give open-chain dienes (4a-e) respectively. The formation of these dienes is explained through ring opening of the cyclobutene formed by 2 + 2cycloadditions of (1 ) and (2). The cyclic ketoketen dithioacetal (9) reacted with (2) to give an unusual compound, which was characterized as thiapyran-2-one (1 0). A plausible mechanism for the formation of (1 0) has been suggested. While the reactions of simple keten 0,O-, S,S-, 0,N-,S,N-, and N,N-a~etals,'-~ and enamines with activated acetylenes have been reported in the literature to proceed through 2 + 2cycloadditions, the conjugated vinylketen 0,O-and dithioacetals with activated acetylenes are known to give either 4 + 2lcycloaddition products or open-chain Michael adduct~.~.' Similarly thioacylketen dithioacetals react with dimethyl acetylenedicarboxylate (DMAD) to give the cor- responding Diels-Alder adducts.8-10 However, the behaviour of polarized ketoketen dithioacetals with DMAD has received very little attention and the easy accessibility of these com- pounds from a wide variety of active methylene compounds warrants a systematic investigation. The present study was therefore undertaken as a part of our interest in the chemistry of ketoketen dithioacetals.' When the ketoketen dithioacetal (la), derived from aceto- phenone, was treated with DMAD (2) in benzene at room temperature, it was recovered unchanged.However (1 a) was found to react with (2) in refluxing xylene and, after 20 h, a I : 1 adduct was isolated in 20 yield. The yield of the adduct was further improved to 60 when (la) and (2) were heated neat at 170-180 "C.The 1 : 1 adduct was characterized as the diene (4a), apparently the result of cleavage of the cyclobutene ring (3) arising from the 2 + 2cycloaddition of the reactants (Scheme 1). The corresponding 4 + 2cycloadduct (6) was not detected from the reaction mixture. Of the two possible geometrical isomers (4a) and (5a), the isomeric structure (4a) was assigned on the basis of the chemical-shift value of the vinylic proton.Thus the 'H n.m.r. signal for the vinylic proton which appeared at 6 6.60 in (la) was shifted to lower field (6 7.40) in (4a) indicating strong deshielding due to the cis-methoxycarbonyl group on the adjacent carbon atom. The strong band at 1 630 cm-' in the i.r. spectrum due to the aromatic carbonyl group confirms the open-chain structure (4a), ruling out the formation of the 4 + 2cycloadduct (6). The ketoketen dithioacetals (I b-e) similarly reacted with DMAD (2) under identical conditions to yield the novel push-pull dienes (4b--e), respectively, in 52-58 overall yields.The spectral and analytical data of (4b-e) are des- cribed in Tables 1 and 2 respectively. The mass spectral fragmentations of the dienes (4) showed extremely weak molecular ion peaks (Table I), while the major fragment ions arose from M+ (4) (Scheme 1) via electrocyclic ring closure followed by loss of a methylmercapto group to give even- electron ions (7), which gave the base peaks (M+ -47) (Scheme 1). The cyclic ketoketen dithioacetal(8) having cis-configuration of carbonyl and bismethylthiomethylene groups did not yield any identifiable product under varying conditions. Either the unchanged compound (8) was recovered under mild conditions or an intractable tar was obtained at higher temperature. Similarly (9) and DMAD (2) under mild conditions did not r 'I R E I EC+ 111 -MeSO$Me":MeS 160-170°C5 E E SMe .R SMe or 'XSMe SMe E' 'SMe (5) J (7)(M+-47) 0 SMe react, but they gave a bright yellow crystalline solid in low yield (1604) when the reactants were heated in a steel bomb in xylene.The product was characterized as the thiapyran-2- one (10) (Scheme 2) on the basis of analytical and spectral data. It showed in its mass spectrum, the molecular ion peak at ni/z 360 (72) (C10H1606S).The i.r. spectrum showed two strong absorption bands at 1 740 and 1 720 cm-I which were I100 J. CHEM. SOC. PERKIN TRANS. I 1983 Table 1. Spectral data for dimethyl 4,4-bismethylthio- I -aroyl (or acyl)butadiene-2,3-dicarboxylates(4b-e) r v,,,.(KBr)h (cm-') 7 Yield Arom/ Compound M.P.("C) (I Ester CO alph CO MCDCI3) mlz (4b) (4c) (44 122-1 24 130-132 I 12-1 I 3 52 58 56 I 722, 1 703 I 725-1 704 1710, 1730 1 628 I 625 I 640 2.20 (s, 3 H, SCHj), 2.35 (s, 3 H, SCHJ), 3.6 (s, 2.30(~, 3 H, SCH,), 2.45 (s, 3 H, SCH,), 3.65 (s, 3 H, OCH3), 3.85 (s, 3 H, OCH,), 7.17 (s, 1 H, olefinic), 7.25-7.65 (m, 5 H, aromatic) 3 H, OCH3), 3.8 (s, 3 H, OCH3), 3.9 (s, OCH,), 7.55 (s, 1 H), 6.80-7.75 (m, A2BZ, 4 H aromatic) 3 H, OCH3),3.85 (s, 3 H, OCH,), 7.48 (s, 1 H, olefinic), 7.30-7.40 (m, A2B2, aromatic) 2.22 (s, 3 H, SCHj), 2.43 (s, 3 H, SCHj), 3.65 (s, 366 (8) 396 (2) 319(100) 349 (1 00) 444, 446 (1)397, (W 135-1 36 52 1712, 1685 1 645 2.22 (s, 3 H, SCH,), 2.30 (s, 3 H, SCHj), 2.48 (s, 399 (100)304 (2) 3 H, CH,), 3.67 (s, 3 H, OCH,), 3.88 (s, 3 H, OCH3), 257 (100) 7.67 (s, I H, olefinic) 0 rSMe: :MeS: Me0 ' E =C02Me E I t Scheme 2.due to the ester carbonyl groups. The other strong band at characteristic absorption in the visible region (above400 nm)." 1625 cm-' was assigned to the thiapyran-2-one carbonyl Final confirmation of the thiapyran-2-one structure (10) was group, which is in agreement with the reported values (I 620-derived from its I3C n.m.r. spectrum (Figure). The character- 1 634 cm-').'1*12 The 'H n.m.r. spectrum (CDCI3) exhibited an istic signal at 6 184 was assigned to the thiopyran carbonyl A2B2quartet at 6 3.08 (4 H) due to four methylene protons. carbon, while the thiocarbonyl carbon of pyran-2-thione is The three closely spaced singlets which appeared at 6 3.80, reported to appear at 6 196.'' 3.85,and 3.86 were assigned to the methoxy and two methoxy- The mechanistic pathway for the conversion of (9) into (10) carbonyl protons.The aromatic protons exhibited signals at thus appears to be an interesting series of rearrangements 6 6.79 (d, J 2.5 Hz, 4-H), 6.86 (dd, ./ 7 and 2.5 Hz, 2-H), and (Scheme 3). The formation of cyclobutene uia 2 + 2cyclo-8.02 (d, J 7 Hz, I-H). The U.V. spectrum (MeOH) of (10) addition followed by ring opening and electrocyclic ring showed absorption bands at A,,,,,. 233 (log E 4.08), 310 (4.19, closure in succession to give compound (15) is logical. The 336 (4.20), and 348sh nm (3.99), thus ruling out the alter- intermediate (1 5) appears to undergo either an interesting native pyran-2-thione I3*I4 structure (12), which shows 1,5-suprafacial shift of the methylthio group or a stepwise J.CHEM. SOC. PERKIN TRANS. I 1983 Table 2. Analytical data for compounds (4b-e) Analysis Calc. (Found ) r-*-Compound Mol. formula C H 4.91 (4.45) 5.07 (5.3)3.82 (3.55) 5.26 (5.35) S (12) 00 Figure. 13C N.m.r. chemical shifts of compound (10) in CDCL (measured at 40 MHz) recorded as 6 (p.p.m.) C-1 133.5d C-7 129.3 C-14 146.2 C-2 112.5d C-8 144.5 C-15 55.3~~ C-3 161.0 C-9 136.0 C-16 163.4 C-4 114.9d C-10 143.1 C-17 164.8 c-5 C-6 34.3 26.9t C-12 (2-13 184.0 138.9 C-18 C-19 52.6q 52.6q H Scheme 3.elimination-addition process leading to the dihydropyran intermediate (16). In the subsequent steps, the intermediate (16), which is susceptible to electrocyclic ring opening, undergoes cleavage to give an activated S-methyl ester intermediate (1 7), which on intramolecular ring closure and elimination of dimethyl sulphide yields the thiopyranone (10). The mass spectrum of (10) exhibited an interesting frag- mentation pattern. The molecular ion peak at m/z 360 (72) was followed by the most intense peak at m/z 328 (M+ -32, loo, C17H120S), which is possibly due to the ion (11) (Scheme 3). Although the loss of methanol in preference to the carbon monoxide in (10) appears to be unusual,16 the presence of the adjacent methoxycarbonyl favours elimination of methanol to give the ion (ll), as shown in Scheme 3.'' Experimental 1.r.spectra were determined on a Perkin-Elmer 297 spectro- photometer, while the U.V. spectrum was run on a Beckmann UV-26 spectrophotometer. IH N.m.r. spectra were deter-mined on a Varian EM-390 90 MHz n.m.r. spectrometer using Me4 as internal reference. Reactions of Aryl (or AlkyZ) 3,3-Bis(methylthio)vinyl Ketones (1 a)-( 1 e) with Dimethyl Acetylenedicarboxylate (2).-(a) Reaction of 2,2-bismethylthiovinyl p-methyl phenyl ketone (la) with DMAD (2) in xylene. A solution of the ketone (la) (2.38 g, 0.01 mol) and DMAD (2) (3.7 g, 0.22 mol) in dry xylene was refluxed for 20 h. Xylene was evapo- rated off under reduced pressure and the residue was chro- matographed on a silica-gel column. Elution with benzene- hexane (1 : 1) yielded dimethyl l,l-bismethylthio-4-(p-toluoyZ)-buta-l,3-diene-2,3-dicarboxylate(4a) (0.76 g, 20) as pale yellow solid which was crystallised from ether-hexane, m.p.110-1 12 "C, vmx. (KBr) 1 728,1708, and 1 630cm-'; G(CDC1J 2.2 (s, 3 H, SCHj), 2.35 (s, 3 H, SCH3), 2.4 (s, 3 H, CH3), 3.65 (s, 3 H, OCH3), 3.85 (s, 3 H, OCH3), 7.4 (s, 1 H, vinylic), and 7.05-7.60 (m A2B2, 4 H, arom) (Found: C, 56.4; H, 5.55. C18HZ005S2requires C, 56.84; H, 5.26). (b) Generalprocedure. A mixture of the keten dithioacetal(1) (0.01 mol) and DMAD (2) (0.02 mol) was heated at 170-180 "C for 6-7 h until the starting material had dis- appeared completely (t.1.c.).The reaction mixture was passed through a silica-gel column. Elution with benzene-hexane (1 : 1) yielded pure compounds (4a-e), which were further purified by crystallization from ether-hexane (Table 1). Reaction of (9) with DMAD (2).-A solution of compound (9) (2.1 g, 0.008 mol) and DMAD (2) (1.42 g, 0.1 mol) in dry xylene (20 ml) was heated in a sealed tube at 160-170 "C for 33 h. Xylene was removed under reduced pressure and the residue was chromatographed on a silica-gel column. Elution with 6 ethyl acetate in hexane gave compound(l0) as a bright yellow crystalline solid (0.43 g, 16), m.p. 141-143 "C (spectral data in text) (Found: C, 60.25; H, 4.75; S, 8.55. Ci!jH1606S requires C, 60.0;H, 4.75; S, 8.88); m/z 360 (M+,72), 329 (53), 328 (loo), 313 (19.7), 300 (14), 272 (14), 269 (27.7), 243 (19), and 242 (44).Acknowledgements We are thankful to Dr. S. M. S. Chauhan, University of Alberta, Edmonton, Canada for the mass spectra and Dr. (Mrs) J. Bannerjee, University of Calcutta for the 13Cn.m.r. spectrum. References 1 Part 21, S. Apparao, A. Rahman, H. Ila, and H. Junjappa, Sjwthesis, 1982, 792. Part 20, S. Apparao, A. Rahman, H. Ila, and H. 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