ENANTIOSELECTIVE PREPARATION OF BETA-ALKYL-GAMMA-BUTYROLACTONES FROM FUNCTIONALIZED KETENE DITHIOACETALS

An efficient and general enantioselective synthesis of beta-alkyl-gamma-butyrolactones has been developed. The key step of this procedure is an oxazolidinone-directed alkylation of a lithiated ketene dithioacetal that proceeds with excellent regiochemical control and high diastereofacial selectivity. Reductive removal of the chiral auxiliary followed by acid-induced cyclization of the resultant hydroxy ketene dithioacetal gives the enantiomerically pure beta-alkyl-gamma-butyrolactone.