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Mechanistic and Kinetic Studies of the Direct Alkylation of Benzylic Amines: A Formal C(sp3)–H Activation Proceeds Actually via a C(sp2)–H Activation Pathway

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journal contribution
posted on 17.12.2015, 07:14 by Robert Pollice, Navid Dastbaravardeh, Nada Marquise, Marko D. Mihovilovic, Michael Schnürch
Mechanistic investigations of a Rh­(I)-catalyzed direct C–H alkylation of benzylic amines with alkenes, formally an C­(sp3)–H activation, reveal this reaction to proceed via imine intermediates and, hence, via C­(sp2)–H activation. The reaction shows a primary kinetic isotope effect of 4.3 at the benzylic C–H position together with a reversible H–D exchange at the same position, which indicates that there are at least two distinct steps in which the corresponding C–H bonds are broken. The imine intermediates are shown to be converted to the final product under the reaction conditions, and a time course analysis of the alkylated imine intermediate shows that it is formed before the final amine product in the course of the reaction.