Construction of tetrahydro-beta-carboline skeletons via Bronsted acid activation of imide carbonyl group: syntheses of indole alkaloids (+/-)-harmicine and (+/-)-10-desbromoarborescidine-A

Indole, a pi-nucleophile, reacts with Bronsted acid activated imide carbonyl group in an intramolecular fashion via a 6-exo-trig cyclization, to deliver a condensed tetrahydro-beta-carboline unit. This methodology is effectively applied to assemble the tetra-hydro-beta-carboline skeleton containing alkaloids such as harmicine and 10-desbromoarborescidine-A.