The functionalization of a cascade of C(sp2)-H/C(sp3)-H bonds: synthesis of fused dihydropyrazoles via visible-light photoredox catalysis

The functionalization of a cascade of C(sp(2))-H/C(sp(3))-H bonds in aldehyde hydrazones with simple 2,2-dibromo-1,3-dicarbonyls was achieved via visible-light photoredox catalysis. This method, which involves free radical addition, polar crossover and 6 pi electrocyclic reaction, provides an efficient approach for the synthesis of complex fused dihydropyrazoles and related derivatives with moderate to good yields and excellent regioselectivity under mild reaction conditions.