The reaction mechanisms for the enantioselectivity and the influence of substituents and spacial configurations in asymmetric branched-oxazaborolidine-catalyzed reductions of acetophenone have been studied by using AMI MO method and transition state theory. The result shows that the boron-catalyzed reactions consists of two similar parallel reactions in which the reactant (r5) of the title compound and the boron-catalysts (rl-r4) generate enantiomers [P(/0 and P(S)] via transition states [Ts(/0 and Ts(S)] and intermediate products [lnp(7?) and Inp( S) ], respectively. The enantioselectivity is determined by the ratio of the rate constants of the two reactions. The determining factors of the rate ratio come from the joint contribution of the activation enthalpy and the activation entropy. In the reactions the reduction products of acetophenone are mainly in configuration R. When N (3) and B(2) of the oxazaborolidine ring have no substituents, the substituents connecting with C(4) orC(5) and their configurations are the main influence factors, especially in that of C (5), on the enantioselectivity in asymmetric boron-catalyzed reduction reactions. The computational results are in consistence with experiments

Key words: oxazaborolidine, REDUCTION, ACETOPHENONE, SELECTIVITY, SELECTIVITY