Aryl Pyrazoles from Photocatalytic Cycloadditions of Arenediazonium

A photocatalytic synthesis of 1,5-diaryl pyrazoles from arenediazoniums and arylcyclopropanols is reported. The reaction proceeded under mild conditions (rt, 20 min) with catalytic [Ru(bpy)(3)](2+) under blue-light irradiation and exhibited compatibility with several functional groups (e.g., I, SF5, SO2NH2, N-3, CN) and perfect levels of regiocontrol. Mechanistic studies (luminescence spectroscopy, CV, DFT, radical trapping, quantum yield determination) documented an initial oxidative quenching of the excited photocatalyst and the operation of a radical-chain mechanism.