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

Reported herein is the development of a photochemical method which allows for the construction of 2-azanorbornane scaffolds from cyclopropylsulfonamide derivatives. Access to the amine radical cation of these species is promoted by a Lewis acid additive which enables the ring opening of the cyclopropylamine moiety to initiate a cascade radical cyclization sequence. Notably, the method allows access to substituted 2-azanorbornane derivatives at all possible carbon centers and A1,3 stereocontrol is observed for C3 substituted derivatives. Preliminary mechanistic investigations suggest an integral role for the Lewis acid additive in facilitating single-electron transfer and avoiding deleterious dealkylation of the starting material. Thus, this method constitutes a modular, mild, and operationally simple approach to privileged saturated aza-heterocycles.