Dynamic Kinetic Resolution of Secondary Alcohols

Significance

The authors present an efficient and highly enantioselective lipase/aluminum-catalyzed dynamic kinetic resolution (DKR) of secondary alcohols. The substrate racemization is catalyzed by a complex made of AlMe₃ and 1,1′-bi-2-naphthol (binol) or 2,2′-biphenol, followed by an enantioselective acylation in the presence of lipase, to give optically active acetates in high to excellent yields and enantioselectivities. This process was successfully applied to aromatic and aliphatic (cyclic as well as acyclic) secondary alcohols. Bisphenol-type ligands proved to be required to achieve high reactivity and selectivity. It has been postulated that they increase the activity of the aluminum catalyst by impeding aggregation. Moreover, bisphenol aluminum complexes maintain their activity towards racemization of the alcohol in the presence of lipase.