A Formal (3+2) Cycloaddition Strategy toward 2-aza-Norbornanes

We report a photochemical strain-release strategy for the synthesis of 2-azanorbornanes from N-cyclopropylsulfonamide derivatives. Under acridinium photoredox catalysis in the presence of ZnCl2, single-electron oxidation of the cyclopropylsulfonamide initiates a radical cascade that furnishes the bridged aza-bicyclic core under mild conditions. The method provides modular access to substitution at C1, C3, C4, C5, and C7 of the 2-azanorbornane scaffold and delivers C3-substituted products with complete endo diastereoselectivity, complementary to the selectivity typically observed in aza-Diels-Alder approaches. The reaction is amenable to continuous-flow scale-up, and the resulting products can be converted into valuable 2-azanorbornane building blocks, including C1 and C3-endo α-amino acid derivatives. Mechanistic studies support a key role for ZnCl2 in enabling productive single-electron oxidation and identify product degradation pathways that inform reaction optimization. Overall, this work establishes a modular and operationally simple entry to a privileged saturated aza-heterocycle.