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Density Functional Theory Study on the Mechanism of Iridium-Catalyzed Benzylamine ortho C–H Alkenylation with Ethyl Acrylate.

ABSTRACT: Iridium-catalyzed oxidative o-alkenylation of benzylamines with acrylates was enabled by the directing group pentafluorobenzoyl (PFB). Density functional theory calculations were performed to explore the detailed reaction mechanism. The calculated results reveal that N-deprotonation prior to C–H activation is favored over direct C–H activation. Moreover, C–H activation is reversible and not the rate-determining step, which has been supported by the experimental observation. The regio- and stereoselectivity of ethyl acrylate insertion are controlled by the steric effect and the carbon atom with a larger orbital coefficient of the ?* antibonding orbital in the nucleophilic attack, respectively. The migratory insertion of ethyl acrylate is computationally found to be rate-determining for the whole catalytic cycle. Finally, the seven-membered ring intermediate IM11 undergoes a sequential N-protonation and ?-H elimination with the assistance of AcOH, rather than ?-H elimination and reductive elimination proposed experimentally, to afford the o-alkenylated product. IM11 is unable to directly cyclize through C–N reductive elimination because both sp3-hybridized N and C atoms are unfavorable for N–C reductive elimination. The origin of the directing group PFB preventing the product and intermediates undergoing aza-Michael addition has been explained.

SUBMITTER: Wang J

PROVIDER: S-EPMC7331057 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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