Mechanism, Regio-, and Diastereoselectivity of Rh(III)-Catalyzed Cyclization Reactions of N-Arylnitrones with
Yingzi Li1,2, Chunhui Shan1, Yun-Fang Yang2
1School of Chemistry and Chemical Engineering, Chongqing University , Chongqing 400030, People's Republic of China.
Abstract:
Nitrones have been used for rhodium-catalyzed cyclization C-H bond activation and O atom transfer of arylnitrones with alkynes by Chang et al. ( J. Am. Chem. Soc. 2015 , 137 , 4908 - 4911 ). Density functional theory method has been used to study the mechanism, regio-, and diastereoselectivity of type reactions. The results elucidated that the reaction pathway for Rh(III)-catalyzed cyclization of N-arylnitrones with alkyne contains a C-H bond activation, an alkyne insertion into Rh-C bond, a reductive elimination to form a Rh(I) complex, an oxidative addition leading to N-O cleavage, an imine insertion into the Rh-C bond, and the final protonolysis to regenerate the products and the active catalyst. The regioselectivity of this reaction with asymmetric alkyne is controlled by the electronic effect in alkyne insertion type instead of steric effects. The distortion-interaction analysis is also used to explain the regioselectivity. The diastereoselectivity is controlled by the imine insertion step. In this step, the sterically less hindered transition state is favored, leading to stereoselective product formation.
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