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In the present paper, the ab initio molecular orbital computations of the enantioselective reduction of 3,3-dimethyl butanone-2 with borane catalyzed by chiral oxazaborolidine (the CBS catalyst) are performed by means of the Hartree–Fock method at the 6-31G∗ basis sets and the structures and properties of the oxazaborolidine catalyst and the catalyst–borane–3,3-dimethyl butanone-2 adducts are studied. Chiral oxazaborolidine is of a twisted chair structure and reacts with borane to form the catalyst–borane adduct whose formation reaction is exothermic. The formation of the catalyst–borane adduct causes the BBH3–HBH3 bond in the borane moiety to be weakened considerably. The catalyst–borane adduct reacts with 3,3-dimethyl butanone-2 to generate the catalyst–borane–3,3-dimethyl butanone-2 adducts. The catalyst–borane–3,3-dimethyl butanone-2 adducts have two stable structures. One is of a twisted boat structure and the other of a twisted chair structure. The formation of the catalyst–borane–3,3-dimethyl butanone-2 adducts results in a great increase in the carbonyl bond length in the 3,3-dimethyl butanone-2 moiety. In addition, there is a quite weak interaction between CCO and HBH3 in the catalyst–borane–3,3-dimethyl butanone-2 adducts. These results are beneficial to the hydride transfer from the BH3 moiety to the carbonyl carbon of 3,3-dimethyl butanone-2. |
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