A study on the stereoselectivity of C,O bond formation in esterification of cyclic thiohydroxamic acids

Abstract

Esterification of cyclic thiohydroxamic acids, for example, N-hydroxypyridine-2(1 H)-thione, N-hydroxy-4-methylthiazole-2(3 H)-thione, and N-hydroxy-4-( p-chlorophenyl)-thiazole-2(3 H)-thione, occurred with inversion of configuration at the attacked stereocenter, as evident from the use of chiral alcohols, alkyl p-toluene sulfonates, and cyclic sulfates. Stereochemical analysis of enantiomerically pure O-alkyl thiohydroxamates was performed on the basis of CD-spectroscopy and chemical derivatization. The assignment of the relative configuration in cyclic O-esters was feasible via NMR spectroscopy, whereas chiral aliphatic glycolato monoesters required hydroxyl group derivatization with chloro-(4 R,5 R)-bis[(1 R,2 S,5 R)-menth-1-yloxycarbonyl)]-1,3,2-dioxaphospholane for this purpose.