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.