Organophotoredox-mediated Formal [3+2]-Cycloaddition of 2H-Azirines with Aryldiazonium Salts: Direct Access to Trisubstituted 1,2,4-Triazoles.

The present work documents an organophotoredox-mediated formal [3+2]-cycloaddition of 2H-azirines with aryl diazonium tetrafluoroborate salts to furnish 1,3,5-trisubstituted 1,2,4-triazoles. The reaction furnishes a regioisomeric mixture of 1,2,4-triazoles in case of unsymmetrically substituted azirines. It is noteworthy that aryl radical generation from diazonium salt under visible light photoredox conditions could be successfully avoided by carefully selecting the reaction conditions.