Styrene—amine and stilbene—amine intramolecular addition reactions

Two mechanisms have been reported for the intermolecular photochemical addition reactions of styrenes and stilbenes with amines. Direct irradiation results in electron-transfer quenching of the singlet styrene by the amine, followed by hydrogen transfer and radical pair coupling. Electron-transfer-sensitized irradiation results in the formation of the styrene or stilbene cation radical which undergoes nucleophilic attack by amines. The intramolecular analogues of these reactions have been investigated and are found to provide a versatile method for the synthesis of nitrogen heterocycles. The synthetic aspects of these reactions are discussed in the context of their reaction mechanisms.