Visible Light Driven Photocascade Catalysis: Ru(bpy)3(PF6)2/TBHP-Mediated Synthesis of Fused β-Carbolines in Batch and Flow Microreactors.

1,2,3,4-Tetrahydro-β-carbolines were coupled with α-keto vinyl azides through an unprecedented visible light-Ru(bpy)3(PF6)2/TBHP mediated photocascade strategy that involves photosensitization, photoredox catalysis and [3 + 2] cycloaddition reaction. The scope and scale-up feasibility of the photocascade strategy was demonstrated by synthesizing 18 different fused β-carbolines in moderate to good yields using batch and continuous flow microreactor. This operationally simple synthetic protocol allows the formation of one C-C and two C-N new bonds in the overall transformation.