Visible Light-Initiated Catalyst-Free One-Pot, Multicomponent Construction of 5-Substituted Indole Chromeno[2,3-b]pyridines

A visible light-initiated pseudo four-component reaction of salicylaldehydes, indole and malononitrile in aqueous ethyl lactate is described. This pot, atomic and step economic (PASE) methodology provides a practical approach for the preparation of various 5-substituted indole chromeno[2,3-b]pyridines from readily available starting materials at ambient temperature without any catalyst. High yields and excellent functional groups tolerance are observed.