Recent Development on the Synthesis of Benzo[b]- and Naphtho[b]furans: A Review

Over the past twenty years benzo- and naphtho[b]furan synthesis has been a widely studied topic, certainly due to the presence of this structural unit in many biologically active compounds. Most of the known methods of the synthesis of these heterocycles are based on an intramolecular cyclization of various open-chain precursors. There are four possible ways of the cyclization and they are based on a formation of appropriate furan bonds: O-C2, C2-C3, C3-b and O-b. The following paper presents these four methods of synthesis of benzo[b]- and naphtho[b]furans which have been developed over the last years.