Four secondary alcohols of different steric environment reacted with five carboxylic acids of different acidity in the presence of N,N,N',N'-tetramethylazodicarboxamide and tributylphosphine to give the corresponding epi-esters in better yield than with diethyl azodicarboxylate-triphenylphosphine in most cases. Of special merit is the combination of the new reagent system with p-methoxybenzoic acid to achieve complete inversion of sterically congested secondary alcohols.