New efficient synthesis of benzofuro[2,3-b]pyrroles utilizing a reactive nitrilium trapping approach by an acid-promoted cascade addition/cyclization sequence

Abstract

The first p-TSA·H₂O-catalyzed highly efficient one-pot cascade reaction for the synthesis of novel fused tricyclic benzofuro[2,3-b]pyrroles has been discovered. The reaction sequence involves a Knoevenagel condensation of 2-hydroxybenzaldehydes with aroylacetonitrile followed by subsequent nucleophilic addition of the divalent isocyano carbon to generate highly reactive nitrilium carbon, which could be readily trapped by an adjacent phenolic group of 2-hydroxybenzaldehydes to access diverse benzofuro[2,3-b]pyrroles in one pot. This approach features a robust one-step protocol with broad substrate scope, good functional group tolerance, and promising application prospects in the synthesis of complex tricyclic N-heterocycles.