Novel chemoselective tosylation of the alcoholic hydroxyl group of syn-alpha,beta-disubstituted beta-hydroxy carboxylic acids.

[small beta]-Hydroxy acids were readily converted into [small beta]-tosyloxy acids (hydroxyl group activation) in moderate to excellent yields via the O,O-dianions generated by treatment with methyllithium and thus make it possible to prepare anti[small alpha],[small beta]-disubstituted [small beta]-lactones directly from the syn aldols.