Intramolecular trapping reactions of vinylsulfenic acid tautomers of enethiolisable sulfines

摘要

J. CHEM. SOC. PERKIN TRANS. 1 1994 Intramolecular Trapping Reactions of Vinylsulfenic Acid Tautomers of Enethiolisable Sulfines Germana Mazzanti,*ea Esther van Helvoirt,a,b Leonard A. van Vliet,a,b Rene Ruinaard,a,b Stefan0 Masiero,a Bianca F. Boninia and Binne Zwanenburg *eb a Dipartimento di Chimica Organica 'A. Mangini: Universita di Bologna, Viale Risorgimento 4, 40 136 Bologna, Italy Department of Organic Chemistry, NSR Center, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands ~~~ ~~ ~ Thermal intramolecular cyclisation of enethiolisable (allylsulfanyl)sulfines affords 2-alkylidene-I ,3-dithiolane I-oxides in good yields. The formation of these compounds is explained by an initial tautomerisation of the sulfine to vinylsulfenic acid, followed by an intramolecular addition of the sulfenic acid to the allylic double bond.Also, sulfines having an S-(prop-2-ynyl) substituent have been investigated and they similarly give 2-alkylidene-5-methylene-I,3-dithiolane 1-oxides. The results obtained by using thionyl chloride to promote the reaction turned out to be highly dependent upon the structure of the starting sulfine. Sulfines (thioketone oxides) of the type A, having a hydrogen at the a-carbon atom are of special interest as they can undergo enethiolisation to their vinylsulfenic acid tautomers B (Scheme 1). Although tautomerisation of sulfines has received little +=+H A B Scheme 1 attention in the literature, the majority of sulfines investigated in the past three decades lacking the necessary a-hydrogen atom,' the vinylsulfenic acid tautomer B of sulfines was explicitly mentioned2 in a discussion of the structure of naturally occurring ethylsulfine, the principal lachrymatory factor of freshly cut onions.Although, earlier, the lachrymator was thought to be prop-1 -enesulfenic acid (H,CCH=CHSOH) its identity as ethylsulfine,2 has now been firmly established., The intermediacy of ethenesulfenic acid was proposed in the thermal reaction of tert-butyl vinyl sulfoxide with methyl pr~piolate.~The formation of thiolane 1-oxide derivatives from prop-2-enesulfenic acid and alkynes was explained by invoking the tautomerisation of intermediate sulfines to the correspond- ing vinylsulfenic acids.s Alkylations of vinylsulfenate anions obtained by a-deprotonation of a sulfine, to give vinyl sulfoxides have also been reported.6 In order to gain more insight into the occurrence and chemical behaviour of the vinylsulfenic acid tautomer of sulfines, we designed an enethiolisable sulfine with an additional functionality that, at least in principle, would react with the tautomeric form. For this purpose, the allylsulfanyl and prop-2- ynylsulfmyl groups were chosen as sulfine substituents. This paper' deals with the preparation and the intramolecular reactions of the sulfines 1and 2 derived from the corresponding dithio esters (Scheme 2). Results and Discussion The dithioates 3 and 4, readily obtained from Grignard reagents and carbon disulfide, followed by alkylation with the appro- priate ally1 or prop-2-ynyl bromide, respectively (Scheme 3),* were oxidised with rn-chloroperbenzoic acid (MCPB) to give the sulfines 1 and 2, respectively.The intramolecular reaction of these upon thermolysis in toluene or in the presence of thionyl chloride has been investigated. Therrnolytic Reactions.-Thermolysis of isopropyl(allylsu1- fany1)sulfine la in boiling toluene for 16 h gave cis-2-isopropylidene-5-methyl-1,3-dithioiane 1-oxide 5a (Scheme 4) (13%), the yield of which was considerably improved (to 72%) when the reaction was conducted in the presence of a catalytic amount (1 0 mol%) of pyridinium toluene-p-sulfonate (PPTS). The structure of the product Sa, established on the basis of its elemental analysis and spectral characteristics,' was unambig- uously confirmed by both an experiment in which a deuterium labelled isopropyl(allylsulfany1)sulfinewas used and by an X- ray diffraction analysis." The formation of product 5a can be explained in terms of an initial tautomerisation of the sulfine la to the corresponding vinylsulfenic acid 6a, followed by an intramolecular addition of the sulfenic acid moiety to the olefinic bond (see Scheme 4).This stereochemical relationship between the sulfinyl oxygen atom and the newly formed methyl group at C-5 in the dithiolane S-oxides was deduced from LIS experiments9 with Eu(fod), on 5a and 5b, as well as from the X-ray analysis on 5a.The cis-relationship found strongly 9710 suggests that the addition of sulfenic acid to the double bond proceeds by a concerted syn-intramolecular process, namely by a six-electron sigmatropic rearrangement.Such a cycloaddition was also proposed for the intramolecular addition of a sulfenic acid to an olefin by Jones et a1.5." Because of this concerted course of the cyclisation, it seems plausible that PPTS functions 3300 J. CHEM. soc. PERKIN TRANS. 1 1994 R’ isopropylidene-5-methylene-1,3-dithiolane 1-oxide 7a could be R2p g x isolated (Scheme 5); with prolonged reaction times only tars H I- 1 S :i+SMgX H 3 4 a -e as for 1 a, b as for 2 iv 1 2 Scheme 3 Reagents: i, CS,; ii, CH,=C(R3)CH,Br; iii, CHSCH,Br;iv, MCPBA H 1 6 5 only in the first step, that is in promoting the enethiolisation of the sulfine.The sulfines 1b-e when thermolysed in toluene under conditions identical with those used for la (refluxing toluene and 10 mol% of PPTS) gave the dithiolane S-oxides 5be in 43, 88,42 and 9%yield, respectively (Scheme 4). The low yield of 5e may be attributed to the difficult enethiolisation of le as was found for methyl thiones.I2 Having established the course of the intramolecular reaction of allylsulfanyl substituted sulfines la-e, we turned our attention to analogous prop-2-ynylsulfanyl substituted sulfines 2a and b. In contrast to our expectation, the cyclisation of 2a and b was best effected in the absence of PPTS in refluxing toluene; in fact, the presence of PPTS lowered the yields.The sulfine 2a, when thermolysed in refluxing toluene for 5 h, gave a tarry product mixture from which only 6% of 2- L 2 8 a R’=R2=Me b R’= Pr, R2 = H 7 Scheme 5 were produced. The use of the strongly acidic catalyst trifluoroacetic acid (TFA) in boiling toluene (5 h) increased the yield of 7a to 18%. Thermolysis of sulfine 2b in refluxing toluene for 5 h gave a 70% yield of (E + Z)-2-butylidene-5-methylidene-1,3-dithiolane 1-oxide 7b while in the presence of PPTS (10 mol%) the yield was reduced to 56%. A lower thermolysis temperature (boiling THF) gave even lower yields of 7b: 17% with PPTS and 48% without PPTS. Formation of the products 7a and b, the structures of which were assigned on the basis of accurate mass measurements and spectral characteristics (see Experimental section), can be under- stood in the same terms as the formation of the products 5, the intermediacy of vinylsulfenic acids 8a and b being assumed, the triple bond of which undergoes intramolecular cycloaddition. Comparison of the results obtained with allylsulfanyl and prop-2-ynylsulfanyl substituted sulfines reveals that the double bond is more reactive in the intramolecular cycloaddition than the triple bond.This difference in behaviour is in contrast with the report by Jones et al. in which it is shown that alkyne-o- sulfenic acids obtained by thermolysis of o-(tert-butylsulfiny1)- alkynes, cyclise to 2-methylidenethiacycloalkane 1-oxides in high yield. Probably, the differences in geometry of the two types of substrates are responsible for the difference in behaviour.In fact, two endocyclic sp2 carbon atoms are present in the products 7, but only one in the case of 2-methylidene- thiacycloalkane 1-oxides. In the present case, the rather low reactivity of the triple bond allows more side reactions to take place; in this, PPTS-catalysis may play a role. Thus, if the cycloaddition is relatively slow, sulfenic acids can undergo a variety of reactions contributing to the multiplicity of products. l4 Reactions with Thionyl Chloride.-Still et al. described the use of thionyl chloride to accomplish an intermolecular reaction between enethiolisable sulfines and alkenes or alkynes. It was, therefore, of interest to use this reagent for the intramolecular reaction of our substrates 1 and 2.Reaction of la with thionyl chloride (1 equiv.) in the presence of 2,6-dimethylpyridine (1 equiv.) in dichloromethane at ambient temperature for 5 h, gave the cyclic product 4-chloromethyl-2-isopropylidene-1,3-dithiolane 9 (46%) the structure of which was supported by analytical and especially NMR spectral data (see Experimental section). There was no significant improvement in yield in the presence of chloride ions J. CHEM. SOC. PERKIN TRANS. I 1994 (with benzyltrimethylammonium chloride or lithium chloride 54% of 9 was obtained). The formation of product 9 can readily be explained in terms of an initial conversion of the vinylsulfenic acid tautomer 6a into the mixed anhydride 10 which, by loss of sulfur dioxide, gives the sulfenyl chloride 11.Subsequent intramolecular reaction of this with the allylic double bond produdes the isolated compound 9 (Scheme 6). When the same reaction was 3=ys %,,Cl IFS PO% Ho\S la 6a 10 kso,/-a 9 11 Scheme 6 attempted with butyl(allylsu1fanyl)sulfine lc only a complex mixture of many products was obtained, even at -25 "C. The reaction of prop-2-ynylsulfanylsulfine 2a with thionyl chloride under the conditions used for la gave only brown tars. A lower reaction temperature, uiz. -20 "C gave only a 13% yield of sulfenyl chloride 12, which clearly results from the tautomer 8a via the mixed anhydride 13 and subsequent loss of sulfur dioxide (Scheme 7).)A1'=)As1'O+ Ho\ 2a 8a SOCI,I 13a 12 Scheme 7 The reaction of butyl(prop-2-ynylsu1fanyl)sulfine 2b with thionyl chloride (I equiv.) in the presence of 2,6-dimethylpyr-idine (1 equiv.) in dichloromethane at room temperature for 1 h, gave a mixture of products from which only one could be separated and identified, uiz. the dithiine 14 (33% yield). The structure of this unexpected product 14 was assigned on the basis of spectral analysis (see below). Its formation can be envisaged * as described in Scheme 8. The vinylsulfenyl chloride 15 arising from 2b in the manner illustrated in Scheme 7, is0 s b-s:' CI //4so -d 2b 13b 1s" -.p, 16 151-HCI PCl S?S' -HCI S 17 S 14 Scheme 8 undergoes a dimerisation in which one molecule acts as a nucleophile and the other one as an acceptor.Subsequent loss of two molecules of hydrogen chloride from the initial adduct 16 produces the bis-dithioester 17 which cyclises to the dithiine 14. The double-bond isomer of compound 17, which is also conceivable, may not be capable of cyclisation. Support for the final cyclisation step is obtained from the MNDO calculations * On the basis of the formation of the dithiine 14 it is suggested that the by-product 'B' of the reaction of 4-trimethylsiloxythiochrom-3-enewith thionyl chloride (ref. 15) has the following structure: 3302 performed by Fabian et ~1.'~on l,;-dithiines. whic I demonstrate that the isomeric open-chain co :ijugated dithione:, of the type 17 are thermodynamically less stable than tfie corresponding cyclic dithiines.The spectral features a1 e iilsc) informative about the structure of 13, espccially the I3CNMR spectra. The lowest field signals in the 13C NMR spcctrun: (CDCI,) were observed at n' 147.92 and 148.39 ppm, while for a S-C=S unit a value of m. 230 ppm would have been expected. The observed values are bctter in agreement with a C=C-S unit ((f 6 154.1 for C-5 in 4-yhenyl-I .2-dithiole-3-thionej '" encountered at C-3 md C-6 in 14. It should bc noted that two distinct carbon signals were also observed for the quaternary carbons C-4 and C-5, namely at d 132.02 and 137.87 ppm. Also the signals for the prop-l-ynylsulFmy1 side chains art.doubled both in the 'H and '-'C NMR spectrum. The same holds for the 'H NMR signals of the propyl chains (see Experimental section). Such doubling of signals in 13C NMR spectra of 1,2-ditbiines has also been reported by Fabian c: and has been explaitled in terms of two non-plamr conforiiiations of the six-mcmbered heterocyclic molecule. Extended TLC aiiaiysix of product 13 showed that it was a single product. The results obtained in the rcaction of prop-2-ynylsylfanyl- substituted sulfines 2a, b with thionyl chloride reveal that the triple bond is not capable of undergoing a cyclisation with a sulfenyl chloride of the type 12 or 15. The formation of the dithiine 14 is an escape reaction for 15 (Scheme 8) which is not possible for 12 (Scheme 7).Concluding Rcwzurks.--The results presented in this paper, together with those reported in the literature, clearly demonstrate that sulfines having a hydrogen atom at the X-carbon, show the propensity to undergo enethiolisation to the corresponding vinylsull'enic acids, provided suitable conditions are chosen. Usually. the tautcin?erir equilibriiirn is at the sulfine side (Scheme 1, A). However, when the vinylsulfenic acids B are transformed into ;Lderivative by an irreversible reaction the equilibrium is shifted to the right-hand side B. The intra- molecular additioii of vinylsulfenic acid to an appropriately positioned olefinic bond is an illustrative example ol' this concept. Experimental Gcncw/ -1R spcclr,A were recorded on a Perkin-Elmer 257 grating spectrometer.'l'he 'H and "C NMR spectra, if not specified, were performed at 200 MHz and at 50.3 MHz, respectively, on a Varian Gemini 200 spectrometer. 60 MHz 'H NMR spectra were recorded with a Varian EM 360L instrumcnt. All NhlR spectra, i1'not specified, were recorded in CDCI, solution. Chemical shifts are given as 0 values relative to tetramcthylsilai~e as the internal standard. Cotipliiig con- stants (J)are quoted in Hz. Mass spectra were recorded with a VG 7070-E spectrometer. The reactions were monitored by TLC performed on silica gel plates (Baker-flex 1B2-F). Column chromatograph) -A as conducted using Merck silica gel 60 (70- 230 mesh). Flash chroniatagraphy was performed on Merch silica gel 60 (230-400 mesh).All reactions were run in dry solvents in an argon atmosphere Light petroleum refers to the fraction with b.p 40-70°C. E,'Z ratios of sulfines were determined on the crude products. In the characterisation of the new compounds, eiemental arialyses were performed tor crystalline products. Oily products linve been characterised by accurate mass measurements. S~ntlii~sisof' the Dit1iiocito.s 3 rind 4.-The dithioates 3 and 4 were prepared using the procedure described by Brandsmi et ril. .I.CHEM. SOC. PERKIN TRANS. I 1994 Ally1 2-methylpropanedithioute3a. Yield 5 1%; yellow oil; b.p. ''? 74 "C at 16 mmHg; v,,,(neat)/cm-' 1202 (C-=S); n',(60 I\ iHz) 1.35 [6 H. d. J 7.0, (CH,),CH], 3.45 [I H, septet, J 7.0, l.Cff3)2CH],3-91(2 Hi d, ,I 6.0, SCH,) and 5.05-6.28 (3 H, m, C'H==CH2):m!z (EI) 160 (M+).I19 (M' .-allyl), 117 (IM'-'.Y) and 87 (Pr'CS) (Fnund: M+, 160.038 !6. CI,H,,S, requires IM,160.038 05). 2-Methylull~vl2-methylpropunedithioate 3b. Yield 1 3%; yellow oil: b.p. 102-104 "C at 16 nimHg; v,,,(CCll,)/c~~n 1170 (C=S); &(60 MHz) 1.36 [6 H, 6, J 7.0. (CH,),CHJ, 1.80 (3 H, s, CH,C=). 3.29 [I H, septei, J 7.0, ((X3)2C1~], 3.92 (2 H, s, SCH,) and 4.93 (2 H, br d, J 6.0.=CH 2); ni,'~(El) I74 (M +), 1 I9 (Pr'CS,) and 87 (Pr'CS) (Found: M '., 174.053 60. C,H,,S2 requires M, 174.03 73). Allvl pentanedithioate 3c. Yield 93:';;; yellow oil; b.p. I 13--115 "C at 16 mmHg; vm,,(CICl,)icm ' I173 (C=S); 6,(60 MHz) 0.89 (3 H, t, J 7.1, CHZ,).1.24-1.48 (2 €-I, m, CH,CH,), 1.68-1.85 (2 H, m, CH,CH2CH,), 3.06(2 Id, t, J7.5.CH,C=S). 3.85(2H,dt,J7.0and1.0,SCH2),5.1';~1H,tid,J6.9andl.O, CHKHH'), 5.28 (I H, dd. .I 10.3 and 1.0, CH=CHI/') and 5.83 (1 H, 111, CH=CH2);m;1:(EI) 174 fM+): 101 (BuCS) and 41 (allyl) (Found: M', 174.053 52. CxH14S2 requires M, 174.053 70). 2-Methylullyl pentunedithioute 3d. Yield 48n4: orange oil purified by flash column chromatography (light petroleum as eluent); ~~,~(CCl~)/crn 1178 (C=S); (S,,iOO MHz) 0.94 (3 H. t, J7.0, CHICH,), 1.1 7-2.22 (7 H, TII,CH,C",CH, + SCH,). 3.07 (2 H, t, J 7.5, CH,CH,CH,CH,!, 3.9.5 (2 H, s, SCH,) and 5.01 (2 H, br d, J 6.0, =CH,): m/::(Ef) 188 (M+), 173 (M' -CH,), 133 (BuCS,), 101 (Bu(3S) and 55 (methylallyl) (Found: M', 188.069 11.C,H,,S, requires h4. 188.069 35). Ally1 ethanedithioute 3e. Yield 357,;;yellow oil; b.p. 74-75 "C at 16 mrnHg: vmax(CCI4)/cm ' 1191 (C:=S);&(60 MHz) 2.83 (3 H, s, CH,), 3.91 (2 H, d, J7.5, SCH,) and 5.06-6.32 (3 H, m. CH-CH,); m/z (EI) 112 (M '). 91 fC'H,CS,j and 59 (CH,C'S) (Found: M+,132.006 53. C,H,S, recyi'iii-esM, 13?.006 75). Prop-2-yn~~l2-rneth~lpropanedithroci1e4a .8b Yield 75%; yellow oil purified by column chromatography (lizht petroleum as eluent); \~,,,(neat)/cm ' 3300 (=C--H), 2120 (CK) and 1202' (C=S): dH(60 MHz) 1.33 [6 FI, d, J 7.5, (CN,)2CH], 2.20 (1 kl, t, J2.8. C-CH), 3.43 [I H. septet. J7.5. (CH,),CHJ and 4.01 (2 M d, J 2.8, SCH,); mi:: (EI) 158 (hl'), 87 (Pr'CS), 71 (HCZCCF!~S) and 43 (Pr') (Found: 1LI --,158.022 30.C,H1,S2 requires M, 158.022 40). Prop-2-ynj-1 pen tnnediili iocrto 4h. Yield 7O';/,; or an ge oiI purified by trash column chromaicgraphy i!ight petroleum as eluent); t~,,,,(CCl,)/cm 3305 (X-H j. 2120 (CS)and 1 i 75 (c=s); dH(60 MHz) 0.84 (3 H, t J 6.5, CH3),1.17--2.11 (4 H, m. CH,CH,CH,), 2.23 (I H, t, 3.0, CKH), 3.05 (2 IH, t, J 7.5.%/ CIf,CH,CH,CH,), 3.96 (2 H, d, J 3.0. CH2C=);m;:(EI) 172 (M+),133 (RuCS,). 101 (BuCS)and 71 (HC=C'CH,S) (Found: +.M 172.037 96. C,H ',SZrequires A+', I72.03Y 05). S.iwt/ie.si.i of' thc Thiokotoiru 0.uirkv (Sultims) I mid 2.--The thioketone oxides 1 and 2 were prepared Dy oxidation with MCPB of the corresponding dithioiites follo~uing the procedure described by Zwaiieiiburg ri iii'.'' AllyI.w@n,t.l isopropjd thioketone o.uidv 1a?.' ' Yield 902; (E:Z = 4: 1); light yellow oil purified by flash column chromatography [light petroleum-diethyl ether (4: I ) as eluent]; vmax(CC14)~cni 1030 and 1 125 (CSO); &(60 MHz) 1.23 [6 H, d, J7.5, CH(CH,),]. 2.92 and 4.10 [l H, 2 m, CH(CH,),. Z and E isomer respectively in a I :J ratio], 3.47 and 4.20 (2 H. 2 d. J 7.5, SCH,, E and Z isomer respectively in ;i 4: I ratio), 5.15-5.40 (2 H, m, =CH,) and 5.65-5.95 (1 H, m, =CFI);HT/Z(E[)!76(M+),i59(M+ -OH). 1?9(M+ -OH -2 CH,) and 87 (Pr'CS) (Found: M', 176.032 61. C,H,,OS, requires M, 176.032 96). J. CHEM. SOC. PERKIN TRANS. 1 1994 Isopropyl 2-methylallylsulfanyI thioketone oxide lb.9 Yield 87% (E:Z= 1:l); light yellow oil purified by flash column chromatography [light petroleum-diethyl ether (4 :1) as eluent]; v,,,(CCl,)/cm~' 1030 and 1105 (CSO); 6,(60 MHz) 1.25 [6 H, d, J 7.0, CH(CH,),], 1.85 (3 H, bs, CH,), 2.90 and 3.60 [l H, 2 m, CH(CH,),, Z and E isomer respectively in a 1:1 ratio], 3.41 and 4.20 (2 H, 2 bs, SCH,, Z and E isomer respectively in a 1:1 ratio) and 5.03 (2 H, m, =CH,); m/z (EI) 190 (M') and 173 (M' -OH) (Found: M', 190.048 38.C8H1,0S2 requires M, 190.048 61). Allylsulfanyl butyl thioketone oxide lc. Yield 85% (E:Z= 2 :3); yellow oil purified by flash column chromatography [light petroleum-ethyl acetate (10 :1) as eluent]; vmaX(CCl4)cm-' 1087 (CSO); &(C,jD,; 60 MHZ) 0.91 and 1.03 (3 H, 2 t, J 7.4, CH,, Z and E isomer respectively in a 3 :2 ratio), 1.10-1.33, 3303 dithiolane 1-Oxides 5from Thioketone Oxides 1.-A solution of freshly prepared thioketone oxide 1 (1.5 mmol) in toluene (10 cm3) was heated at reflux for 16 h in the presence of PPTS (10 molx). The solvent was evaporated off under reduced pressure to leave a dark-yellow oil, which was purified by flash column chromatography [diethyl ether as eluent for 5a, b, e; light petroleum-ethyl acetate (2: 1) for 5c and d]. 2-Isopropylidene-5-methyl-1,3-dithiolane1-oxide 5a.9 Yield 72%; white crystals; m.p.55 "C (from pentane); vmax(CC14)/ cm-' 1045 (SO);6,(200 MHz) 1.55 (3 H, d, J 6.5, 5-CH3), 1.87 (3 H, s, CH,), 2.25 (3 H, s, CH,), 2.98 (1 H, m), 3.31 (1 H, dd, J 11.5 and 5.5) and 3.70 (1 H, td, J 11.5 and 1.5); Sc(50.3 MHz) 11.21 (CH,), 23.17 (CH,), 23.47 (CH,), 36.69 (CH,), 62.01 (CH), 138.16 (C) and 139.43 (C), assignments were made by DEPT; m/z (EI) 176 (M'), 159 (M+ -OH), 86 (Me,CCS) and 1.33-1.55and 1.58-1.78(4H, 3m,CH,CH2CH3),2.16(1.2H,71 (MeCCS) (Found: C, 47.7; H, 6.8; S, 36.0.C7Hl,0S, t, J 7.5, CH,CSO, Z isomer), 2.91-3.09 (2 H, m, CH,CSO E isomer and SCH, Z isomer), 4.05 (0.8 H, dt, J 6.8 and J 1.0, SCH, E isomer), 4.92-5.42 (2 H, m, =CH,) and 5.45-5.96 (1 H, 2 m, =CH); mlz (EI) 190 (M'), 173 (M' -OH), 101 (BuCS) and 41 (allyl) (Found: M+, 190.048 22. C8Hl,0S, requires M, 190.048 61). Butyl 2-methylallylsulfanyI thioketone oxide Id. Yield 70% (E:Z = 44 :56); yellow oil purified by flash column chromato- graphy [light petroleum-diethyl ether (4: 1) as eluent]; v,,,-(CC1,)jcm ' 1088 (CSO); 6,(60 MHz) 0.88 and 0.90 (3 H, 2 t, J 6.5, CH,, Z and E isomer respectively in a 56 :44 ratio), 1.17- 1.66(4 H, m, CH,CH,CH,), 1.76 and 1.81 (3 H, 2 s, CH,C=, E and Z isomer respectively in a 44: 56 ratio), 2.48 and 2.89 (2 H, 2 t, J 7.5, CH,CS, Z and E isomer respectively in a 56 :44 ratio), 3.36 and 3.93 (2 H, 2 s, CH,S, E and Z isomer, respectively, in a 44: 56 ratio) and 4.82-5.0 (2 H, m, XH,); m/z (EI) 204 (M'), 187 (M' -OH), 101 (BuCS), 55 (methylallyl) (Found: M', 204.064 01.C9H ,OS, requires M,204.064 26). Allylsulfanyl methyl thioketone oxide le. Yield 60% (E:Z = 2:l); yellow oil purified by flash column chromatography (dichloromethane as eluent); vma,(CCl,)/cm-' 1090 and 1070 (CSO); aH(6O MHz) 2.33 and 2.48 (1 H, 2 s, CH,, Z and E isomer respectively in a 1 :2 ratio), 3.53 and 3.88 (2 H, 2 d, J 6.5, CH,S, E and Z isomer respectively in a 2 :1 ratio) and 5.00-6.36 (3 H, m, CHSH,); m/z (EJ) 148 (M+), 131 (M+ -OH), 59 (MeCS) and 41 (allyl) (Found: M+, 148.001 45.C,H,0S2 requires M, 148.001 66). Isoprop-vl prop-2-ynylsulfanyl thioketone oxide 2a. Yield 85% (E:Z = 3 :2); light yellow oil purified by column chromato- graphy [light petroleum-diethyl ether (4: 1) as eluent]; v,,,(CCl,)lcm~' 3250 (-C-H), 2120 (Cg) and 1100 (CSO); 6,(60 MHz) 1.24 and 1.27 [6 H, 2 d, J 7.0, CH(CH,),, E and Z isomer respectively in a 3: 2 ratio], 2.33 and 2.47 (1 H, 2 t, J2.7, XH, Zand E isomer respectively in a 2 :3 ratio), 2.99 and 4.10 [l H, 2 septets, J 7.0, CH(CH,),, Z and E isomer respectively in a 2: 3 ratio] and 3.54 and 4.33 (2 H, 2 d, J 2.7, SCH,, E and Z isomer respectively in a 3:2 ratio); m/z (EI) 174 (M'), 157 (M' -OH), 87 (Pr'CS), 71 (SCH,C=CH) and 43 (Pr') (Found: M', 174.017 13.C7HloOS2 requires M, 174.017 31). Propyl prop-2-ynylsulfanyl thioketone oxide 2b. Yield 80% (E:Z = 1 :1); yellow oil purified by flash column chromato- graphy [light petroleum-ethyl acetate (10: 1) as eluent]; v,,,(CCl,)/cm ' 3305 (=C-H) and 1090 (CSO); 6,(60 MHz) 0.94 (3 H, t, J 6.5, CH,), 1.14-1.88 (4 H, m, CH,CH,CH,), 2.23-2.74 (2 H, m, rCH and CH,CSO Z isomer), 2.95 (1 H, t, J 7.0, CH,CSO, E isomer) and 3.48 and 4.10 (2 H, 2 d, J 3.0, SCH,, E and Z isomer respectively in a 1 :1 ratio); mp (EI) 188 (M'), 171 (M' -OH), 101 (BuCS) and 71 (SCH2CrCH) (Found: M+, 188.032 61. C8Hl,0S, requires M, 188.032 96).General Procedure for the Preparation of 2-Alkylidene- 1,3- requires: C, 47.69; H, 6.86; S, 36.37%). 2-Isopropylidene-5,5-dimethyl-1,3-dithiolane 1 -oxide 5b.' Yield 43%; colourless oil; v,,,(CCl,)/cm 1050 (SO); 6&00 MHz) 1.23 (3 H, s, CH,), 1.54 (3 H, s, CH,), 1.87 (3 H, s, CH,), 2.25 (3 H, s, CH,), 2.98 (1 H, d, J 11.5) and 3.84(1 H, d, J 11.5); 6,(50.3 MHz) 19.62 (CH,), 19.95 (CH,), 23.45 (CH,), 23.86 (CH,), 42.75 (CH,), 65.35 (C), 138.36 (C) and 139.90 (C), assignments were made by DEPT; m/z (EI) 190 (M +)and 173 (M' -OH) (Found: M', 190.048 34. C,H,,OS, requires M, 190.048 61).2-Butylidene-5-methyl- 1,3-dithiolane 1-oxide 5c. Yield 53% (E:Z = 83 :17); greenish-yellow oil; v,,,(CCl,)/cm ' 1050 (SO); 6&00 MHz) 0.82 (3 H, t, J 7.3, CH,CH,), 1.26-1.51 (5H, m, CHCH, and CH,CH,), 1.93-2.09 and 2.36-2.50 (2 H, 2 m, =CCH,, E and Z isomer respectively in an 83 :17 ratio), 2.78-3.06(1 H,m,CHCH,),3.20-3.33(1 H,dd,J11.3and5.0), 3.45-3.63 (1 H, m) and 5.93 and 6.32 (1 H, 2 t, J 7.5, =CH, Z and E isomer respectively in a 17: 83 ratio); 6,(50.3 MHz) 10.95 (CH,), 13.37 (CH,), 21.10 (CH,), 33.41 (CH,), 36.53 (CH,), 60.77 (CH), 134.08 (CH) and 145.66 (C), assignments were made by DEPT; m/z (EI) 190 (M'), 173 (M' -OH) and 100 (PrCHCS) (Found: M', 190.048 29). C8Hl,0S2 requires M, 190.048 61). 2-Butylidene-5,5-dimethyl-1,3-dithiolane 1-oxide 5d.Yield 42% (E:Z = 74:26); pale green oil; v,,,(CCl,)/cm~' 1058 (So);6&00 MHz) 0.98 (3 H, t, J 7.5, CH,CH,), 1.27 and 1.31 (3 H, 2 s, one methyl from SCCH,, Zand Eisomer, respectively, in a 26 :74 ratio), 1.44-1.66 (5 H, m, one methyl from SCCH, and CH,CH,), 2.09-2.24 and 2.51-2.64 (2 H, 2 m, XCH,, E and Z isomer, respectively, in a 74 :26 ratio), 2.98 and 3.07 (1 H, 2 d, J 11.8, one H from SCH,, Z and E isomer, respectively, in a 26 :74 ratio), 3.79 and 3.83 (1 H, 2 d, J 1 1.8, one H from SCH,, E and Z isomer, respectively, in a 74: 26 ratio) and 6.1 1 and 6.47 (1 H, 2 t, J 7.8, =CH, 2 and E isomer respectively in a 26: 74 ratio); 6,(50.3 MHz) 13.62 and 13.89 (CH,, E and Z isomer), 19.59 and 20.31 [SC(CH,),, E and Z isomer), 21.62 and 22.99 (CH,, Z and Eisomer), 33.87 and 34.94 (CH,, Eand Z isomer), 42.61 and 42.77 (CH,, E and Z isomer), 64.53 and 65.77 (SC, E and Z isomer), 135.23 and 135.38 (=CH, E and Z isomer) and 145.04 (XS, E and Z isomer), assignments were made by DEPT; m/z (EI) 204 (M'), 187 (M' -OH) and 100 (Pr'CHCS) (Found: M+, 204.064 10.C9H160S, requires M, 204.064 26). 5-Methyl-2-methylidene- 1,3-dithiolane 1-oxide 5e.Yield 9%; yellow oil; vmaX(CCl,)/cm-' 1050 (SO); dH(200 MHz) 1.43 (3H,d,J6.7,CH3),3.08-3.25(1H,m,CHCH,),3.35(1 H,dd,J 11.7 and 5.2), 3.58 (1 H, dd, J 11.7 and 9.9, 5.68 (1 H, d, J2.3) and 5.93 (1 H, dd, J 2.3 and 0.7);Sc(50.3 MHz) 10.61 (CH,), 36.69 (CH,), 60.29 (CH), 115.75 (=CH,) and 153.06 (C), assignments were made by DEPT; m/z (EI) 148 (M'), 131 (Mf -OH) and 58 (CH,CS) (Found: M', 148.001 51.C5H80S2 requires M, 148.001 66). General Procedure for the Preparation of 2-Alkylidene-5-methylidene- 1,3-dithiolane 1-Oxides 7 from Thioketone Oxides 2.-A solution of freshly prepared thioketone oxide 2 (1.5 mmol) in toluene (10 cm3) was heated at reflux for 5 h as such or with added catalyst (10 mol% PPTS or TFA). The solvent was evaporated off under reduced pressure to leave a dark oil, which was purified by flash column chromatography [light petroleum-ethyl acetate (2: 1) as eluent]. 2-lsopropylidene-Smethylidene-1,3-dithiolane 1-oxide 7a. Yield 0% (with PPTS present), 6% (without catalyst), 18% (with TFA present); dark brown oil; ~,,,(CCl,)/cm-~ 1047 (SO); dH(200 MHz) 1.90 (3 H, S, CH,), 2.27 (3 H, S, CH,), 3.88 (I H, d, J 12, SCHH'), 4.52 (1 H, dt, J 12.0 and 2.0, SCHH'), 5.74 (1 H, m, =CHH') and 5.91 (1 H, m, XHH'); dc(50.3 MHz) 24.18 (2 CH,), 36.20 (CH,), 120.09 (=CH,), 133.40(C), 140.70 (C) and 154.36 (C), assignments were made by DEPT; m/z (EI) 174 (M'), 157 (M' -OH), 86 (Me,CCS) and 71 (MeCCS) (Found: M', 174.017 10.C,H,,OS, requires M, 174.017 31). 2-Butylidene-5-methylidene-1,3-dithiolane1-oxide7b. Column chromatography of the crude product from the reaction without catalyst gave first the E isomer (66% yield) then the 2 isomer (4% yield) as pale brown oils; from the reaction with PPTS present only the E isomer was obtained in 56% yield; E-7b: v,,,(CC~,)/cm-' 1082 (SO); dH(200 MHZ) 0.85 (3 H, t, J 7.5, CH,), 1.31-1.52 (2 H, m, CH,), 2.01-2.18 (2 H, m, CH,), 3.82 and4.1l(2H,ABq,Jl3.3,SCH2),5.67(1H,d,JlS,=CHH'), 5.79 (1 H, d, J 1.5, SHH') and 6.27 (1 H, t, J 7.5, =CH); 6,-(50.3 MHz) 13.34 (CH,), 21.37 (CH,), 32.1 1 (CH,), 32.46 (CH,), 117.70(=CH,), 132.01(CH=), 140.58(C) and 151.36(C), assignments were made by DEPT; m/z (EI) 188 (M'), 171 (M' -OH) and 100 (PrCHCS) (Found: M', 188.03275.C,H,,OS, requires M, 188.032 96); 2-7b: v,,,(CCl,)/cm 1055 (SO); d,(60 MHz) 0.96 (3 H, t, J 6.5, CH,), 1.17-1.83 (4 H,m,2 CH,), 3.86 and 4.39(2 H, AB q,J13.3, SCH,), 5.78 (1 H, s, =CHH'), 5.95 (1 H, s, =CHH') and 6.12 (1 H, t, J7.5, =CH); mjz (EI) 188 (M'), 171 (M' -OH) and 100 (PrCHCS) (Found: M', 188.03280.C,H,,OS, requires M, 188.032 96). General Procedure for the Reaction of Thioketone Oxides 1 and 2 with Thionyl Chloride.-The solution of 2,6-dimethyl-pyridine (1.5 mmol) and thionyl chloride (1.5 mmol) in dichloromethane (4 cm3) was added to a solution of freshly prepared thioketone oxide (1.5 mmol) in dichloromethane (4 cm3). The mixture was stirred for 1-5 h and then washed with 1 mol dm-, HCl, followed by saturated aqueous sodium hydrogen carbonate and brine. The organic phase was dried, concentrated under reduced pressure and the residue was chromatographed on silica gel (light petroleum as eluent). 4-Chloromethyl-2-isopropylidene-1,3-dithioIane9. From thio- ketone oxide la; reaction time 5 h at room temp.; yield 46%; yellow oil; v,,,(CCl,)/cm~l 2920, 1621, 1430, 1370, 1261, 1197, 1085, 1042, 910 and 833; dH(200 MHz) 1.72 (3 H, S, CH,), 1.75 (3 H, s, CH,), 3.36 (1 H, ddd, J 12, 4.5 and 1.1, SCHH'), 3.47-3.58 (2 H, m, SCHH' and CHH'CI), 3.73 (1 H, pseudo t, J 11 and 11, CHH'Cl) and 3.84-3.96 (1 H, m, CHCH,CI); 6,(50.3 MHz) 24.53 (CH,), 24.70 (CH,), 39.77 (CH,), 44.92 (CH,), 53.71 (CH), 120.99(C) and 125.61 (C), assignments were made by DEPT and by I3C-lH shift correlation; m/z (EI) 194 (M'), 179 (M' -CH,), 159 (M' -Cl), 145 (M' -CHlCl), 118 (M' -CH,CHCH,Cl), 86 (Me,CCS) and 71 (MeCCS) (Found: M', 193.998 48.C7H,,ClS2 requires M, 193.999 07). 1-(Prop- 2 -yn y lsulfan y 1)-2-methy lp rop-1-enesu lfen y 1 chloride 12. From thioketone oxide 2a; reaction time 4 h at -20 "C; yield 13%; yellow oil; ~,~~(CCl~)/cm-~ 3305 (=C-H) and 1217; dH(200 MHz) 1.97 (3 H, s, CH,), 2.08 (3 H, s, CH,), 2.32 (1 H, t, J2.6, CXH) and 3.62 (2 H, d, J2.6, CH,C=CH); m/z (EI) 192 J.CHEM. SOC. PERKIN TRANS. I 1994 (M'), 157 (M' -Cl), 118 (Me,CCS,), 86 (Me,CCS) and 71 (MeCCS) (Found: M+, 191.983 21. C,H,ClS, requires M, 191.983 43). 3,6-Bis(prop-2-ynylsulfanyl)-4,5-dipropyl-1,2-dithiine 14. From thioketone oxide 2b; reaction time 1 h at room temp.; yield 33%; yellow oil; v,,,(CCl,)/cm-' 3300 (=C-H); d,(200 MHz) 0.98 and 1.00 (6 H, 2 t, J 7.0, 2 CH,), 1.45-1.65 (4 H, m, 2 CH,CH3), 2.28 and 2.33 (2 H, 2 t, J2.6, 2 CSH), 2.60-2.75 (4 H, m, 2 CH,CH,CH,) and 3.47 and 3.59 (4 H, 2 d, J 2.6, 2 CHZCKH); dc(50.3 MHz) 14.58 (2 CH,), 24.59 (2 CHZCH,), 27.17 and 27.67 (2 CH,C=CH), 30.94 (2 CH,CH,CH,), 73.08 and 73.27 (2 CKH), 79.21 and 79.83 (2 CSH), 132.02 and 133.87 (2 C=CS) and 147.92 and 148.39 (2 C=CS), assignments were made by DEPT; m/z (EI) 340 (M+), 301 (M+ -CH,CSH), 269 (M' -SCH,C=CH) and 198 (M' -2 SCH,C=CH) (Found: M', 340.044 43.Cl6HZ0S4 requires M, 340.044 79). References 1 For reviews see: (a) B. Zwanenburg, Recl. Trav. Chim. Pays-Bas, 1982,101,l;(b) Phosphorus Sulfur Silicon Relat. Elem., 1989,43,1; (c) B. G. Lenz and B. Zwanenburg, in Methoden Org. Chem. (Houben-Weyl), Band El 1, Organische Schwefelverbindungen, Georg Thieme, Stuttgart, 1985, p. 911; (d) E. Block, in Organic Sulphur Chem., eds. R. Zh. Freidlina and A. E. Shorova, Pergamon Press, Oxford, 1981, p.15. 2 (a)A. I. Virtanen and C. G. Spare, Suom Kemistil B, 1961,34,72;(h) T. Moisio, C. G. Spare and A. I. Virtanen, 1962, 35, 29; (c) A. I. Virtanen and C. G. Spare, Acta Chem. Scand., 1963,17,641; (d) A. I. Virtanen, Angew. Chem., 1962,74,374; (e)Phytochem., 1965,4, 207. 3 (a)M. H. Brodnitz and J. V. Pascale, J. Agric. Food Chem., 1971,19, 269; (b) E. Block, L. K. Revelle and A. A. Bazzi, Tetrahedron Lett., 1980,21, 1277; cf 1(d). 4 E. Block, R. E. PennandR. K. Revelle, J.Am. Chem. Soc., 1979,101, 2200; cf A. G. W. Baxter and R. J. Stoodley, J. Chem. SOC., Chem. Commun., 1976, 366. 5 (a)R. Bell, P. D. Cottam, J. Davies, D. N. Jones and N. A. Meanwell, Tetrahedron Lett., 1980, 21, 4379; (b) D. N. Jones, in Perspectives in the Organic Chemistry of Sulfur, eds.B. Zwanenburg and A. J. H. Klunder, Elsevier, Amsterdam, 1987, p. 189. 6 (a)G. E. Veenstra and B. Zwanenburg, Recl. Trav. Chim. Pays-Bas, 1976,95, 37; (6) 1976,95,202. 7 Part of this work was published in a preliminary form, see ref. 9. 8 (a)J. Meijer, P. Vermeer and L. Brandsma, Recl. Trav. Chim. Pays- Bas, 1973, 92, 601; (6) J. Meijer, P. Vermeer, H. J. T. Bos and L. Brandsma, Red. Trav. Chim. Pays-Bas, 1973,92, 1067. 9 G. Mazzanti, R. Ruinaard, L. A. Van Vliet, P. Zani, B. F. Bonini and B. Zwanenburg, Tetrahedron Lett., 1992,33, 6383. 10 J. Smits, P. T. Beurskens, L. A. Van Vliet, G. Mazzanti and B. Zwanenburg, Crystallogr. Spectrosc. Rex, 1994, 24, in print. 11 D. N. Jones, D. R. Hill, D. A. Lewton and C. Sheppard, J. Chem. Soc., Perkin Trans. I, 1977, 1574. 12 D. Paquer and J. Vialle, Bull. Soc. Chim. Fr., 1969, 3595. 13 R. Bell, P. D. Cottam, J. Davies and D. N. Jones, J. Chem. Soc., Perkin Trans. I, 1981, 2106. 14 E. Block and J. O'Connor, J. Am. Chem. Soc., 1974,96,3929. 15 I. W. J. Still, D. V. Fraser, D. K. T. Hutchinson and J. F. Sawyer, Can. J. Chem., 1989,67, 369. 16 J. Fabian and P. Birner, Collect. Czech. Chem. Commun., 1988, 53, 2096 and references therein. 17 N. Plavac, I. W. J. Still, M. S. Chauhan and D. M. McKinnon, Can. J. Chem., 1975,53,836. 18 B. Zwanenburg, L. Thijs and J. Strating, Red. Trav. Chim. Pays-Bas, 1967,86,577. 19 P. MetznerandT. H. Pham,J. Chem. Soc., Chem. Commun., 1988,390. Paper 4/03675A Received 17th June 1994 Accepted 25th July 1994