1-Alkyl-3-alkylindolin-2-imine hydrochlorides as useful building blocks in the copper-catalyzed synthesis of polycyclic indoline scaffolds.

A novel and efficient copper-catalyzed synthesis of dihydro-6 H -indolo[2,3- b ]quinoline derivatives has been developed by using 3-alkyl-1-alkylindolin-2-imine hydrochlorides as the building blocks. Furthermore, easy reduction of dihydro-6 H -indolo[2,3- b ]quinolines with diisobutylaluminum hydride provided tetrahydro-6 H -indolo[2,3- b ]quinoline derivatives in excellent yields. The present method shows some advantages including use of cheap cuprous chloride as the catalyst and tolerance of wide functional groups.