Theoretical Studies on the Asymmetric Baeyer-Villiger Oxidation Reaction of 4-Phenylcyclohexanone with m-Chloroperoxobenzoic Acid Catalyzed by Chiral Scandium(III)-N,N '-Dioxide Complexes

摘要

The mechanism and enantioselectivity of the asymmetric Baeyer-Villiger oxidation reaction between 4-phenylcyclohexanone and m-chloroperoxobenzoic acid (m-CPBA) catalyzed by Sc-III-N,N-dioxide complexes were investigated theoretically. The calculations indicated that the first step, corresponding to the addition of m-CPBA to the carbonyl group of 4-phenylcyclohexanone, is the rate-determining step (RDS) for all the pathways studied. The activation barrier of the RDS for the uncatalyzed reaction was predicted to be 189.8kJmol(-1). The combination of an Sc-III-N,N-dioxide complex and the m-CBA molecule can construct a bifunctional catalyst in which the Lewis acidic Sc-III center activates the carbonyl group of 4-phenylcyclohexanone while m-CBA transfers a proton, which lowers the activation barrier of the addition step (RDS) to 86.7kJmol(-1). The repulsion between the m-chlorophenyl group of m-CPBA and the 2,4,6-iPr(3)C(6)H(2) group of the N,N-dioxide ligand, as well as the steric hindrance between the phenyl group of 4-phenylcyclohexanone and the amino acid skeleton of the N,N-dioxide ligand, play important roles in the control of the enantioselectivity.