Formal Insertion of a Metal Carbene Complex into a -Carbon-Carbon bond. Gold-catalyzed synthesis of 3H-indoles

We report here a formal insertion of a metal carbene complex in a single carbon-carbon bond. This behavior occurs with the participation of an alpha-imino gold carbene complex, generated from benzofused triazapentalenes or, in a one-pot procedure, from their 1-propargyl-1H-benzotriazole precursors, and gold-catalytically activated ynamides. As the result, 3H-indole derivatives were obtained, with formation of a quaternary center. A computational analysis carried out on the reaction mechanism indicates that the bulkiness of the gold ligand plays a key role forcing a conformation, which includes aromatic interactions, that favors the approximation of the carbenic carbon to the reactive site. In addition, a negative crossover experiment rules out a cationic arene migration pathway.