含侧链手性噁唑硼烷催化还原苯乙酮对映选择性的理论研究

用AMI方法研究了含侧链手性恶唑硼烷催化苯乙酮还原反应的对映选择性机理 及其取代基和构型对对映选择性的影响。计算结果表明，含侧链手性恶唑硼烷催化 还原苯乙酮的反应机理与Corey等人提出的机理相符合，在此类硼催化剂的作用下 ，苯乙酮还原产物的绝对构型以R型为主。当恶唑硼烷环N(3)，B(2)上无取代基时 ，C(4)，C(5)位的取代基及其构型是不对称催化反应对映选择性的主要影响因素。

Theoretical Study on the Enantioselectivity in Asymmetric Branched- Oxazaborolidine-Catalyzed Reductions of Acetophenone

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