Regiodivergent Control in the Gold(I) Catalyzed Synthesis of 7-Pyrazolylindoles from 1-Propargyl-1H-benzotriazoles and Ynamides through α-Imino Gold(I) Carbene Complexes

A smooth, gold catalyzed, atom-economical and regioselective synthesis of indoles is reported here. The reaction occurs from a nucleophilic attack of insitu synthesized triazapentalenes to gold activated ynamides and involves the participation of alpha-imino gold carbene complexes. The use of sulfonyl ynamides drives the reaction to the formation of 2-amidosubstituted indoles. However, the employment of 2-oxazolidinolylynamides allows the formation of both isomers, such as, 2-amido- and 3-amidosubstituted indoles. In this case, the regioselection could be controlled by a correct choice of the catalyst ligand and the electron-donating capability of the aryl substituent of the ynamide. A correct control in both parameters permits a totally regioselective synthesis of one or the other regioisomer. Isolation of key intermediates and X-ray analysis allowed for a plausible explanation for this behavior.