Aza- and carbo-[3+3] annulations of exo-cyclic vinylogous amides and urethanes. Synthesis of tetrahydroindolizidines and an unexpected formation of hexahydroquinolines
Keywords: Aza-[3+3] annulation; Carbo-[3+3] annulation; Vinylogous amides; Quinolines; Tetrahydroindolizidines;