Photoredox‐Catalyzed Strain‐Release Annulation of N ‐Cyclopropylamides With Diazenes

Pyrazolidines are valuable saturated N–N heterocycles, yet convergent routes from independently variable C3 and N2 components remain limited, particularly when mono‐donor cyclopropanes are employed as C3 synthons. Herein, we report a visible‐light photoredox‐catalyzed strain‐release annulation of mono‐donor N ‐cyclopropylamides with diazenes. The transformation integrates single‐electron‐transfer oxidation of N ‐cyclopropylamides with strain‐driven cleavage of an otherwise electronically unbiased C─C σ bond and dual C─N bond formation, providing direct access to 3‐amidopyrazolidines bearing a cyclic N ‐acyl aminal motif. A broad range of aryl, heteroaryl, aliphatic, and drug‐derived N ‐cyclopropylamides, together with azodicarboxylates, diaryl diazenes, azodicarboxamides, and a cyclic azo reagent, are compatible under mild, metal‐free conditions. Preliminary reactions with N‐ sulfinylamines and an N ‐cyclobutylamide furnish five‐ and six‐membered N,S ‐heterocycles, suggesting that this photoredox platform may be applicable to other heteroatom–heteroatom π components.