Synthesis of chiral 3-acyl-4-alkylthiazolidine-2-thiones as enantioselective acylating agents

R-(-)-3-Benzoyl-4-ethylthiazolidine-2-thione 4a and S-(+)-3-benzoyl-4-isobutylthiazolidine-2-thione 4b have been easily prepared in 79-90% yield from R-(-)-2-amino-1-butanol la and S-(+)-leucinol 1b, respectively. Compounds 4a,b are useful for enantioselective acyl transfer to amine and amino acid racemates 5a-d in high yields (78-94%) and moderate to good optical purity (48-68% ee). One can monitor the acylation by disappearance of the yellow colour of the acylating agents 4a,b.