S-Methyl dithiocarbonate

S-methyl dithiocarbonate (76S413). Stereoselective isomerization of 1,2-disubstituted alkenes may be achieved by a sequence such as the following fr<2n5-alkene bromo-hydrin -> /3-hydroxythiocyanate -> cw-thiirane -> cw-alkene (75TL2709). 

J. Marco-Contelles, P. Ruiz-Femandez, and B. Sanchez, New annulated furanoses A new free-radical isomerization of an S-methyl hex-5-enylxanthate to an 5-(cyclopentylmethyl) S-methyl dithiocarbonate, J. Org. Chem. 58 2894 (1993). 

Allylimidates underwent a clean Claisen-type rearrangement in the presence of 5 mol % palladium chloride (equation 28),40 as did allyl carbamates39 and S-allylthioimidates (equation 29).41 This S to N rearrangement has found application particularly in the synthesis of pyrimidines, systems for which thermal S to N allylic rearrangements were generally ineffective (equation 30).42 Finally, 0-allyI S-methyl dithiocarbonates cleanly underwent palladium(ll)-catalyzed O to S allylic transposition (equation 31 ).43... 

To a mixture of O-Cyclododecyl S-methyl dithiocarbonate (1.0 mmol), Bu3SnH (320 mg, 1.1 mmol) in benzene (5 ml) was added Et3B (1.1 ml, 1.1 mmol, 1 M hexane solution). The mixture was stirred for 20 min, then the solvent was removed and the residue was chromatographed on silica gel to give cyclododecane in 93% yield [40]. 

Thus secondary or tertiary alcohols ROH can be reduced to RH via their thiocarboxy-lates R C(S)OR, or dithiocarbonates [xanthates, R S(CS)OR the Barton McCombie reaction] 147-149 for example cholesteryl thiobenzoate or S-methyl dithiocarbonate gives cholest-5-ene in 90% and 78% yield respectively (equation 15-47, R = Ph or MeS). The reaction works best for secondary alcohols the 0-t-alkyl xanthates are often rather unstable at room temperature, though the reactions can be carried out at low temperature with initiation by Et3B/02. The primary alkyl xanthates undergo C-O fission only at higher temperatures, when other reactions may compete. The thiocarbonyl imidazolides provide a variant on this theme, and the cholesterol derivative (15-5, R = /V-imidazolc) reacts with tributyltin hydride to give an 18% yield of cholestene.147... 

Table 5.1 Deoxygenation of O-cyclododecyl S-methyl dithiocarbonate with tetraalkylammonium hypophosphites in water.

Further studies of the deoxygenation of alcohols by triplet sensitisation and SET to their S-methyl dithiocarbonates under a variety of conditions have been reported. The properties of 2,4,6-triphenylthiapyrilium tetrafluoroborate as an SET sensitiser have been discussed. The triplet excited state of 6H-purine-6-thione acts as an electron donor for p-dinitrobenzene and as an electron acceptor for tetramethylbenzidine. Photolysis of sulfuryl chloride in the presence of tetramethylsilane yields exclusively Me3SiCH2S02Cl. In the presence of added yttrium(III) chloride or sulfur, the reaction is less selective and Me3SiCH2Cl is also obtained. In contrast the presence of these photocatalysts in the photoreaction of sulfuryl chloride with hexamethyldisiloxane yields solely Me3SiOSi-Me2CH2S02Cl, whereas in their absence Me3SiOSiMe2CH2Cl is also obtained. ... 

Di-0-isopropylidene-3-0-(S-methyl dithiocarbonate)-a-D-glucofuranose Glucofuranose, l,2 5,6-di-0-isopropylidene-, S-methyl dithiocarbonate, a-D- (8,9) (16667-96-2)... 

Lanosteryl S-methyl dithiocarbonate in xylene added during 0.5 hr. under argon to a stirred and refluxing mixture of tributylstannane and xylene, and refluxing continued 2 hrs. -> lanosta-8,24-diene. Y 83%. - This reduction is part of a method for the deoxygenation of sec. alcohols. F. e. and related reactions s. D. H. R. Barton and S. W. McCombie, Soc. Perkin I 1975, 1574. 

Reactions with Alcohols. Treatment of alcohols with sodium hydroxide and CS2 and subsequent reaction with an alkyl halide, usually methyl iodide, leads to O-alkyl S-methyl dithiocarbonates which can be pyrolyzed to alkenes (Tschugaeff reaction) (eq 4). ... 

Treatment of xanthate 39 with tributyltin hydride and AIBN affords die expected product 40 together with the unexpected. S-methyl dithiocarbonate compound 41 wdiich is thought to arise by radical isomerization. ... 

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