Syntheses of azapolycyclic compounds by aminium radical routes: trapping of the radical intermediates

Photolysis of three alkenyl nitrosamines in the presence of oxygen or bromotrichloromethane resulted in the interception of the intermediate C-radicals by these radical trapping agents and the reaction pathways were cleanly diverted leading to the formation of the nitrate esters or halides with pyrrolidine rings as the primary products. The exo-nitrates in the oxidative photolyses decomposed by secondary ionic pathways; these reactions were hydrolysis, nitrous acid elimination and a cleavage reaction (promoted by a β-amino group), among others. The efficiency of the cleavage reaction is controlled by a stereoelectronic factor that requires the participating bonds and the lone-pair nitrogen orbital be oriented in an antiperiplanar conformation. When such a conformation exists in a rigid or semiflexible framework, cleavage occurs extensively. However, in freely rotating acyclic systems, cleavage does not occur even when the required conformation can be attained. Only halides resistant to intramolecular nucleophilic displacement to form the aziridinium intermediates were isolated in the bromotrichloromethane trapping experiments. Other exo-halides underwent solvolysis via aziridinium ion intermediates.