Stereocontrolled construction of octahydroquinolizines, octahydroindolizines, hexahydrobenzo[a]quinolizines, and an octahydroindolo[2,3-a]quinolizine by an intramolecular double Michael reaction: synthesis of (±)epilupinine

Abstract

Stereocontrolled one-step syntheses of octahydroquinolizine and octahydroindolizine derivatives from α,β-unsaturated enamide esters was achieved under two different conditions; heating in the presence of chlorotrimethylsilane, triethylamine, and zinc chloride at 180–185 °C, and treatment with dimethyl-t-butylsilyl trifluoromethanesulphonate in the presence of triethylamine at –78 to 20 °C. A simple synthesis of an alkaloid, (±)-epilupinine, was accomplished. Hexahydrobenzo[a]-quinolizin-4-ones and an octahydroindolo[2,3-a]quinolizin-4-one were also constructed by the same method.