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 the 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 as well as a source of -O- for the installation of regioselective keto functionality in the key reaction intermediate 5-aryl-3,4-dihydrobenzo[a]phenanthridin-1(2H)-one (H) through multicomponent reaction. 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 C=C, one C=N, and two C-O bonds simultaneously in a single step without requiring a base or an activator for the oxygenation process.