DMSO-assisted environmentally benign synthesis of benzo[]-chromeno[4,3,2-]phenanthridines by remote oxidative hetero cross-coupling cyclization and aromatization reaction.

An unprecedented metal-free and catalyst-free synthesis of benzo[]chromeno[4,3,2-]phenanthridine derivatives, a class of 1,6-diheterophenalenoid heterocycle, is reported for the first time. The oxidative cross-coupling reaction for the remote cyclization is achieved through the generated -quinone methide intermediate followed by an electrocyclic ring closure reaction. The aromatization of the cyclohexane ring is achieved by sequential H shift, hydroxylation, and elimination reaction. DMSO-assisted concomitant cyclization and aromatization reactions are also disclosed for the first time.