Thiols from thiocarbonic derivatives

A particular case is the use of a hydrogen sulfide salt instead of the thiol, to effect the fragmentation. Treatment of the thiocarbonate derived from cysteine with 2 equiv of potassium hydrogensulfide in methanol results in the formation of the potassium salt of thiocysteine in 85% yield (eq 2). ... 

Treatment of alkylsulfenyl methyl thiocarbonates derived from alkyl thiols and Scm-Cl with triphenylphosphine at 0 °C in benzene generates 5 alkyl methyl thiocarbonates in good yield (78% for alkyl = benzyl) (eq 13). Arylsulfenyl methyl thiocarbonates do not parallel this behavior vs. triphenylphosphine but they react cleanly with tributylphosphine (e.g., in dioxane-water) to generate the free arylthiol (see below).The reductive cleavage of alkylsulfenyl methyl thiocarbonates with trialkylphosphines (McsP, EtsP, BU3P) can be achieved with practically quantitative yields in protic solvents (THF-water) in the presence of acids... 

The 1-thio-D-glucose derivative (15) has been synthesised from the corresponding free sugar (12) by treatment with 5,5 -bis( 1-phenyl-l f-tetrazoI-5-yl)dithiocarbonate, As indicated in Scheme 3, a thiocarbonate derivative (14) was formed initially with concomitant liberation of thiol (13). Direct attack by this thiol at C-1 (path a) gave the main product (15) in 63% yield, whereas benzyloxy participation in the displacement at C-1 with attack by the nucleophile at C-6 (path b) gave its regio-isomer (16) which was isolated in 33% yield. The use of compound (15) in silver triflate promoted glycosylations is referred to in Chapter 3. 

The synthesis and properties of thiol-ester 5-oxides R C(0)S(0)R have been investigated in a search for new syntheses of sulphenates by 0-alkylation followed by nucleophilic cleavage [R C(0)S(0R )R + Nu R OSR + R C(0)Nu]. In the event, sulphenates were not formed from thiocarbonate 5-oxides (R = OEt) nor from N or S analogues/ or from derived oxo-sulphonium salts. 

When the substrate thiol is suitably substituted in such a way that a nucleophile is present in the y position with respect to the thiol, the sulfenyl thiocarbonate intermediate derived from the thiol and Scm-Cl may cyclize in the absence of acid via intramolecular nucleophilic attack at the pre-existing thiol S (with elimination of COS and methanol). The final product forms through the intermolecular nucleophilic attack of a second thiol at the same sulfur atom, with displacement of the internal nucleophile. ... 

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