Synthesis of Dihydroindoloisoquinolines through Copper-Catalyzed Cross-Dehydrogenative Coupling of Tetrahydroisoquinolines and Nitroalkanes

Lately, the cross-dehydrogenative coupling of tetrahydroisoquinolines and nitroalkanes has become a widely studied reaction in organic chemistry; the corresponding β-nitroamines are generally formed irrespective of the catalysis and activation mode utilized. A quite distinct behavior was observed when the reaction was catalyzed by copper nanoparticles supported on titania, leading to the formation of 5,6-dihydroindolo[2,1-a]isoquinolines with high selectivity and good yields. A meticulous reaction mechanism is proposed, based on experimentation, and discussed along with a key chemical modification of these compounds. Apparently, the catalyst effectiveness resides in its nanostructured character, outperforming the activity of the commercial copper catalysts.