SYNTHESIS, REACTIONS, AND STEREOCHEMICAL CORRELATIONS OF AN OPTICALLY ACTIVE TERVALELENT PHOSPHORUS THIO ESTER

Abstract

The tetracovalent (R)-(−)-isopropyl methylphosphinothionate (2) reacts with methyl trifluoromethanesulfonate to form a phosphonium salt (3), which yields the tervalent (R)-(−)-Oisopropyl S-methyl methylphosphonothioite (4) on treatment with triethylamine. However, the reaction is much less stereospecific (∼35%) than that of the corresponding P=O analog, 1 (∼100%). The (−)-4 product was characterized and its configuration confirmed by conversion into its corresponding P=O and P=S derivatives, (S)-(−)-5 and (R)-(−)-8, respectively, which have which have been related to the known (S)-(−) and (R)-(+)-O-isopropyl methylphosphonothioic acids (6). The triflate product [(−)-4] has also been prepared by a relatively simple asymmetric induction reaction that had been reported for a similar compound, and the stereospecificities of the two procedures are compared.