Quantum chemical study on enantioselective reduction of keto oxime ether with borane catalyzed by oxazaborolidine. Part 1. Structures of catalyst-borane-keto oxime ether adducts

In the present work, quantum chemical computations of the enantioselective reduction of keto oxime ether with borane catalyzed by chiral oxazaborolidi ne are performed by means of the Hartree-Fock and the density functional me thods. The structures of oxazaborolidine, oxazaborolidine-borane adduct, an d oxazaborolidine-borane-keto oxime ether adducts are optimized completely at the HF/6-31g* and B3LYP/6-31g* levels and their properties studied in de tail. The oxazaborolidine catalyst is a twisted chair structure and reacts with borane at the nitrogen site of the catalyst to form the catalyst-boran e adduct whose formation reaction is exothermic. The catalyst-borane adduct reacts easily with keto oxime ether to form catalyst-borane-keto oxime eth er adducts that have eight stable structures. The coordination of the carbo nyl oxygen in keto oxime ether at the boron site of the catalyst is of more advantage to the enantioselective reduction of keto oxime ether than the c oordination of the oxime nitrogen in the keto oxime ether at the boron site is. (C) 2001 John Wiley & Sons, Inc.