Light‐Triggered Nickel‐Catalyzed Azide−Alkyne Cycloaddition for the Preparation of 1,5‐Disubstituted 1,2,3‐Triazoles

When irradiated by UVA, a Ni(II) precatalyst integrating a benzophenone chromophore in its structure catalyzes the regioselective cycloaddition of alkynes and azides to produce 1,5‐disubsituted 1,2,3‐triazoles with 1,5:1,4 regioisomer ratios ranging from 1.7:1 to >20:1. Speciation and reactivity studies revealed that the reaction most likely proceeds through a Ni(I)/Ni(III) catalytic cycle.