Direct access to benzo[b]fluorenes via a gold-catalysed A3-coupling strategy

Abstract

A one-pot atom- and step-economical method for the synthesis of benzo[b]fluorenes, from aldehydes, alkynes and amines, proceeding via an A³-coupling/formal [4 + 2] thermal cyclization is described. The transformation generates water as the only by-product and three new carbon–carbon bonds are simultaneously formed. The scope was demonstrated by the synthesis of 32 benzo[b]fluorenes and, by specific designing of starting materials, regiocontrol could be accessed for some substrates.