Kinetic Resolution of 3-Hydroxy-3-Substituted Oxindoles through NHC-Catalyzed Oxidative Esterification

Abstract

The enantioselective synthesis of 3-hydroxy-3-substituted oxindoles has been extensively studied as they represent the core structure of a large number of natural products and pharmaceuticals. While the majority of previous methods focus on the asymmetric addition of different types of nucleophiles to the corresponding ketones, we have reported an unprecedented and alternative approach, namely catalytic kinetic resolution of this important class of tertiary alcohols to provide, for the first time, 3-hydroxy oxindoles with a wide range of 3-substituents including alkyl, alkenyl, alkynyl and aryl groups in highly enantioenriched form. The excellent level of differentiation of the two tertiary alcohol enantiomers (S up to 78) has been realized through oxidative esterification catalyzed by chiral N-heterocyclic carbene (NHC), with the aid of cooperative ­catalysis by Lewis acid.