Developing Transition-Metal Catalysts for the Intramolecular Hydroamination of Alkynes

Group 7−12 transition-metal complexes serve as effective catalysts for the regioselective intramolecular hydroamination of aminoalkynes having the general formula RC⋮C(CH2)nNH2 (n = 3, R = H, Ph; n = 4, R = H) and of 2-(phenylethynyl)aniline. Primary products are pyrrolidines and piperidines bearing an α-alkylidene functionality and 2-phenylindole, respectively. Isomerization yields the corresponding pyrrolines and 1,2-dehydropiperidines. The catalytic properties of the transition-metal complexes depend on the appropriate choice of ligand, solvent, temperature, and counteranion. Principles for identifying the most active transition-metal catalysts for the hydroamination of alkynes and for optimizing the reaction conditions are developed. The X-ray crystal structure of one catalyst, [PdCl(triphos)](CF3SO3), has been determined.