A quantum chemical study on the mechanism of chiral N-oxides-catalyzed Strecker reaction |
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Authors: | Zhishan Su Song Qin |
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Institution: | Key Laboratory of Green Chemistry and Technology (Sichuan University), Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064, China |
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Abstract: | The mechanism for the Strecker reaction of silyl cyanide (H3SiCN) and benzaldehyde N-methylimine (PhCHNCH3) catalyzed by chiral 3,3′-dimethyl-2,2′-bipyridine N,N′-dioxide was investigated using the density functional theory (DFT) at the B3LYP/6-31G* level. The calculations revealed that the non-catalyzed reaction proceeded in a concerted way via a five-membered ring transition state, while the catalytic one occurred stepwisely via a hexacoordinate hypervalent silicate intermediate. It was predicted that both non-catalyzed and catalytic Strecker reactions involved two competitive reaction pathways, that is, addition followed by isomerization or isomerization followed by addition. The calculations indicated that two reaction pathways were comparable for both non-catalyzed and catalytic Strecker reactions. In the catalytic reaction, the strong electron donor (N-O) of chiral N-oxide played an important role in enhancing the reactivity and nucleophilicity of H3SiCN by coordinating O atom to the Si atom of H3SiCN. Chiral N-oxide could be used as a good catalyst for the reaction, which was in agreement with the experimental observations. |
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Keywords: | Strecker reaction Chiral N-oxide α-Amino nitriles Hypervalent silicate |
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