Formation of Cyclohepta[b]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.