Formation of Cyclohepta[<i>b</i>]indole Scaffolds via Heck Cyclization: A Strategy for Structural Analogues of Ervatamine Group of Indole Alkaloid

Ervatamine, silicine, methuenine, etc., are naturally occurring alkaloids that exhibit antimicrobial, anticancer, and anti-HIV activities. Indole fused with a seven-membered carbocyclic ring is a commonly observed structural feature among this series of bioactive compounds. This work describes a strategic approach for the synthesis of cyclohepta­[b]­indole structural scaffolds. The synthetic strategy consists of a solvent-free Baylis–Hillman reaction of 2-bromobenzaldehydes, followed by iodine-catalyzed C-alkylation of indole with the Baylis–Hillman adducts. Finally, intramolecular Heck coupling reaction using Pd­(OAc)2 as catalyst in the presence of benzyltrimethyl­ammonium bromide under microwave condition produced the desired cyclohepta­[b]­indole derivatives.