手性噁唑磷烷-硼烷催化还原苯乙酮对映选择性的理论研究

应用密度泛函理论BHandH/6-31G**计算方法研究新型手性非金属催化剂1,3,2-噁唑磷烷-硼烷催化还原苯乙酮的对映选择性反应机理, 确定了在反应途径上的反应物、络合物、过渡态, 中间体和对映体中间产物. 计算结果表明, 该对映选择性还原反应是两个平行的分步反应, 对映体产物主要是(R)构型. 采用同样的方法研究了对映选择性还原反应在甲苯中的溶剂化效应. SCRF计算显示, 甲苯溶剂不改变反应的机理, 但能降低各驻点的能量和(R)反应的位垒, 有利于催化还原反应朝生成(R)构型中间产物的方向进行.

Theoretical Study on the Enantioselectvity in a Chiral Oxazaphos-pholidine-borane Catalyzed Reduction of Acetophenone

Density functional (BHandH) calculations, using 6-31G** basis set, have been employed to study the reaction mechanism of the enantioselectivity in a chiral 1,3,2-oxazaphospholidine-borane cata- lyzed reduction of acetophenone. Our calculations confirm that title reaction consists of two parallel step processes, in which complexes, TS, intermediates and enantiomer middle products are located on the enantioselective reaction pathway between oxazaphospholidine borane adduct and acetophenone. In the re- duction products of acetophenone are mainly in (R) configuration. In addition, solvent effects of reaction were studied with the PCM model. It was found that the mechanism did not change as the toluene solvent was in- troduced, but the energies of stationary points and the barriers for the rate-controlling step in (R) reaction were lower than those in the gas phase. This indicates that the enantioselective reaction (R) can take place in solution more easily.