Benzannulation of 2-Alkenylindoles using Aldehydes by Sequential Triple-Relay Catalysis: A Route to Carbazoles and Carbazole Alkaloids

Benzannulation of 2-alkenylindoles with readily available aldehydes, under one-pot sequential triple-relay-catalysis, provides an easy access to several structurally unique carbazoles including 2-and 3-alkenylcarbazoles. This protecting group-free method enabled one-pot synthesis of alkaloids such as hyellazole and 6-chlorohyellazole, and the formal syntheses of seven other alkaloids. Construction of the core structure, present in murastifoline A, murrafoline E, and related alkaloids was also demonstrated. Even conjugated 3,3'-biscarbazoles can also be synthesized by one-pot, two-fold sequential triple-relay catalysis.