Visible light-induced reductive aza-6π electrocyclization access to phenanthridines

Visible light-induced aza-6 pi electrocyclization was developed for the synthesis of aza-arenes from nitroarenes with diverse aldehydes. This protocol allows the reduction of nitroarenes by B2nep2 and subsequent 6 pi-electrocyclization of the in situ formed imine under visible light. An array of 6- and multi-substituted phenanthridines were constructed in moderate to good yields under purple LEDs at room temperature. A wide scope of substrates with diverse functional groups were well tolerated. In addition, the synthetic utility of this methodology was further demonstrated in the late-stage functionalization of celecoxib. A simple, efficient, green method for constructing substituted phenanthridine with nitroaromatic hydrocarbons and aromatic aldehydes and alkyl aldehydes under visible light.