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Rhodium-Catalyzed Hetero-(5 + 2) Cycloaddition of Vinylaziridines and Alkynes: A Theoretical View of the Mechanism and Chirality Transfer

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posted on 2016-02-18, 00:00 authored by Lei Zhu, Xiaotian Qi, Yu Lan
A newly reported density functional theory method, M11-L, was performed to study the mechanism and chirality transfer for the intramolecular formal hetero-(5 + 2) cycloaddition of vinylaziridines with alkynes. Both (E)- and (Z)-olefinic substrates were considered in the density functional theory calculations. The computational results suggested a metallahydropyridine pathway for the generation of azepines, which involves aziridine cleavage, 2π insertion of the alkyne group into the Rh–C bond, and reductive elimination from a rhodium­(III) cation. The chirality transfer process for the (E)-alkene substrate is shown to occur on the re face of the alkene, whereas the (Z)-alkene cycloaddition chirality transfer occurs on the si face. The high enantioselectivity in this type of reaction is attributed to the greater ring strain in the trans allylic rhodium complex.