A rhodium(I)-catalyzed alkylation reaction of benzylic amines via C(sp)-H activation using quaternary ammonium salts as alkyl source is described. The reaction proceeds via in situ formation of an olefin via Hofmann elimination, which is the actual alkylating reagent. This represents an operationally simple method for substituting gaseous and liquid olefins with solid quaternary ammonium salts as alkylating reagents, which is transferable to other C-H activation protocols as well.

C-H alkylation reactions using short chain olefins as alkylating agents could be operationally simplified on the lab scale by using quaternary ammonium salts as precursors for these gaseous reagents: Hofmann elimination delivers in situ the desired alkenes with the advantage that the alkene concentration in the liquid phase is high. In case a catalytic system did not tolerate the conditions for Hofmann elimination, a very simple spatial separation of both reactions, Hofmann elimination and direct alkylation, was achieved to circumvent possible side reactions or catalyst deactivation. Additionally, the truly catalytically active species of a rhodium(I) mediated alkylation reaction could be identified by using this approach.Scheme 1 Murai reaction. † Electronic supplementary information (ESI) available: Detailed experimental procedures and copies of spectra. See