摘要
用AM1方法研究了含侧链手性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 .当唑硼烷环N( 3) ,B( 2 )上无取代基时 ,C( 4) ,C( 5 )
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 AM1 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 (r1～r4) generate enantiomers [P(R) and P(S)] via transition states [Ts(R) and Ts(S)] and intermediate products [Inp(R) 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) or C(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.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
2003年第2期192-197,共6页
Acta Chimica Sinica
基金
云南省教育厅科研基金 (No.0 1 2 2 4 )资助项目
