Synthesis of Octahydro- and Decahydroquinolines by a One-Pot Cascade Reaction of Tetrasubstituted Enecarbamate.

A transition-metal-catalyzed cyclopropanation followed by ring opening was investigated for the synthesis of octahydroquinolines 4 and decahydroquinolines 5 having a quaternary carbon center at the angular position, which are core structures of the fawcettimine-type alkaloids. A tandem reaction was also established for the synthesis of decahydroquinolines 5 and the tricyclic compound 6 through an iminium ion intermediate, readily produced by acidic treatment of cyclopropane 2.