1,3-Diamination of Ary Cyclopropanes with Diazines: A (3+2) Cycloaddition Enabled by Bromide/Photoredox Co-catalysis

<jats:p>A synergistic bromide/photoredox co-catalyzed aza-(3+2) cycloaddition of aryl cyclopropanes with diazenes has been developed. This metal-free protocol enables the direct construction of structurally diverse pyrazolidines under mild conditions. The reaction features broad substrate scope, excellent functional group tolerance, and gram-scale feasibility. Mechanistic studies support a pathway involving bromine radical-induced homolytic substitution (SH2) at the cyclopropane ring followed by C-centered radical addition to the N=N bond, radical-polar crossover (RPC), and SN2 cyclization. This strategy overcomes the long-standing limitation of the use of simple aryl cyclopropanes in diamination cycloaddition reactions and provides a versatile approach to heterocyclic 1,2-diamies in a C(sp3)–C(sp3) bond difunctionalization process.</jats:p>