First synthesis of the chiral mixed O/S ligands, 1,2-sulfinyl thiols: application as chiral proton sources in enantioselective protonations of enolates

A suitable method for the preparation of the chiral mixed O/S ligands 1,2-sulfinyl thiols is described. These compounds have then been used as a chiral proton source in the enantioselective protonation of 2-methyl tetralone enolate and the results are compared with those obtained from the analogous alcohols. A theoretical model is proposed to explain the different behaviors exhibited in the protonation reaction for each of these proton sources. Configurational assignments for the new chiral thiols have been carried out by means of X-ray analysis.