Synthesis of 2-arylchromeno[2,3,4,5-lmna]phenanthridines through a sequential multicomponent assembly, oxygenation and 6πe electrocyclization reactions

Abstract

A novel metal-free synthetic method is presented for 2-arylchromeno[2,3,4,5-lmna]phenanthridines from the one-pot reaction of aryl amine, aromatic aldehyde and cyclic ketone in the presence of 30 mol% (±)-CSA. This protocol efficiently exploits DMSO as a solvent and a source of –O– for the installation of a regioselective keto functionality in the key reaction intermediate 5-aryl-3,4-dihydrobenzo[a]phenanthridin-1(2H)-one (H) through multicomponent reactions. Due to its rigid structure, H facilitates further domino reactions such as 6πe electrocyclization and aromatization, which have not been studied before. The sophisticated aspect of this approach lies in its ability to create two CC, one CN, and two C–O bonds simultaneously in a single step without requiring a base or an activator for the oxygenation process.