The Use of a Rhodium Catalyst/8-Aminoquinoline Directing Group in the C-H Alkylation of Aromatic Amides with Alkenes: Possible Generation of a Carbene Intermediate from an Alkene

Rhodium-catalyzed alkylation reactions of C-H bonds (hydroarylation) in aromatic amides that contain an 8-amino-quinoline as a directing group with alkenes are discussed. Various alkenes, including acrylic esters, styrenes, alpha, beta-unsaturated butyrolactones, dihydrofurans, maleimides, and norbornene derivatives are applicable to this C-H alkylation. The reaction with norbornene gives unusual endo-hydroarylation products in a high degree of selectivity. The use of a carboxylic acid as an additive dramatically increases both the reactivity and the selectivity of the reaction. The results of deuterium-labeling experiments suggest that hydrometalation or carbo-metalation, which are commonly accepted mechanisms for C-H alkylation reactions, are not involved. Instead, the reaction appears to proceed through a rhodium carbene intermediate generated from the alkene.