Photocatalytic Conversion of Aminocyclopropanes to γ-Lactams by Sequential Ring-Expansion and Peripheral Diversification

Rings underpin pharmaceuticals, agrochemicals, and materials, driving renewed interest in skeletal ring expansion. Current skeletal ring expansion strategies mainly focus on single-atom insertion or rearrangement; reliable methods for multiple single-atom insertion and peripheral diversification of saturated small rings are lacking. Herein, we report a general and efficient photocatalytic system directly converting aminocyclopropanes to γ-lactams via sequential C-/N-single-atom [ n + 2] ring-expansion and peripheral diversification. The system accomplishes both γ-lactam formation and subsequent diversification at the γ-position via six distinct bond-forming reactions across hundreds of synthetic examples under predictable reaction conditions. Experimental and computational studies converge on photoredox-mediated radical pathways.