Chemoenzymatic Dynamic Kinetic Resolution of Secondary Alcohols and Amines Employing Copper-Based Photocatalysis

Abstract

A tandem photo- and biocatalytic dynamic kinetic resolution of secondary alcohols and amines was achieved employing a commercially available lipase, Candida antarctica lipase B (CALB), and a heteroleptic copper complex. The process is an example of using copper-based photocatalysis to promote hydrogen atom transfer (HAT) processes employing thiyl radicals. Screening of 48 complexes and 5 disulfides identified Cu(dtbbpy)(DPEPhos)BF4 and (Ph3SiS)2 as an optimal catalyst system to promote the HAT process. The catalytic system represents a general system for radical-mediated racemization applicable to both aliphatic and aromatic alcohols and amines (18 examples, 60 → 97% yield, 76 → 99% ee).