Dual Role of the Rhodium(III) Catalyst in C–H Activation: [4 + 3] Annulation of Amide with Allylic Alcohols to 7-Membered Lactams

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[4 + 3] annulation of primary and secondary benzamide and cinnamamide derivatives using allyl alcohol as a coupling partner catalyzed by Rh(III) is reported, where Rh(III) is playing a dual role of an oxidant and a catalyst for C-H activation. The Rh-catalyst oxidizes allyl alcohol to its carbonyl derivative, and the in situ-generated carbonyl compound reacts with benzamide in the presence of the Rh-catalyst, forming the corresponding alkylated products. Mechanistic studies show that AgSbF₆ is also playing a dual role. Apart from being a halide scavenger, AgSbF₆ catalyzes the cyclization of the alkylated product, forming the desired lactam. The current method has good synthetic application and is useful for synthesizing a few biologically active compounds that can act as the dopamine D₃ receptor ligand, including berberine-like analogues. The deuteration study and control experiments helped us to propose the mechanism.