中文摘要：

The synthesis of enantiomerically enriched epoxides especially styrene oxides is an interesting challenge1,2 since they are often valuable building blocks for various fine chemical products and pharmaceuticals such as (a)2-, (a)3-, and á1-adrenergic receptor agonists3, 4. In recent years,there has been a flood of papers describing the synthetical methods of the chiral non-racemic epoxides5,6. Here we firstly developed a green, simple and potential epoxidation system by enantioselective reduction of a-haloacetophenones using NaBH4 in water.The procedure of the unexpected epoxidation was firstly found accidentally in the study of L-proline-catalyzed asymmetric reduction of aldehydes, ketones in water. In that time, we observed not only reductive product a-bromophenethyl alcohol but also a small quantity of styrene oxide after three hour reduction of a-bromoacephenone in water. It is impossible to produce the epoxide in the reduction when THF acts as solvent. Then we optimized the reaction conditions and extended reaction time to 5 hr until we obtained the epoxide as a major product.Encouraged by the front results, we tried a-CD as a chiral inducement and catalyst. Cyclodextrins (CDs), a cyclic oligosaccharide composed of several D-glucose units with an a-1, 4 linkage (6, 7, 8for á-, (a)-, (a)-CD, respectively), have been recognized as versatile enzyme mimics since every one molecule of them possesses a hydrophilic outside, which can dissolve in water, and a hydrophobic cavity, which provides an apolar matrix, described as "micro heterogeneous enwronment"7. All the experiments were carried out in water under room temperature. The procedure is a green, simple and potential, although the optically active styrene oxides are obtained in only moderate ees. and yields.When á-bromoacephenone and Sodium Borohydride (1.2 equiv, to ketone) reacts in water using 150mol% (a)-CD as catalyst, a 41% chemical yield and 45% optical yield of the corresponding epoxide were obtained under mild condition.