Thioxoesters synthesis

The enzymatic reduction of a thiocarbonyl compound has been investigated [159] for the first time, in order to provide a new route for enan-tiopure thiols, molecules which are currently needed for asymmetric synthesis. Reaction of easily available /1-thioxoesters with baker s yeast under classical conditions did furnish the expected thiols, but with lower enantiomeric purity and moderate conversion rate, due to the competitive hydrolysis of the thioxo group into a carbonyl leading to an alcohol. However, conditions (ethyl acrylate, dry yeast) were found to improve the production of (S)-ethyl 3-mercaptobutanoate. Cyclic thioxo esters led to high stereoselectivity of cis (1S,2S) products, but with moderate chemical yields. 

The above-mentioned (9-deoxyribosyl thiobenzoate (c/. equation 39) was obtained from 1,5-protected deoxyribose and phenyl dithiobenzoate. ° Also vinyl arenecarbodithioates were shown to be applicable for the synthesis of thioxoesters." ... 

This method can be applied with almost every substituent R and R. Thioxoesters of dicarboxylic acids can also be prepared via the imidates. Fully characterized authentic compounds of this type were, however, not obtained until the 1970s. Synthetic problems arise especially if the thioxoester groups are close enough to each other to permit formation of heterocycles during their synthesis. 

---