The oxazaborolidine-mediated reduction of chiral, 4-substituted 1-trimethylsilyl-1-alkyn-3- ones followed by hydroboration affords syn or anti 3-hydroxy 4-substituted carboxylic acids, common substructures of a number of biologically active macrolides, peptides and depsipeptides, with high control on the new C (3) stereocenter. This strategy has been applied to the synthesis of (3S, 4S)-3-hydroxy-4-methylheptanoic acid and of N-Boc- ...