Electron-Transfer-Initiated Photoreactions of 1-Methyl-2-phenyl-1-pyrrolinium Perchlorate with α-Heteroatom-Substituted Alkanoate Anions

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Abstract
The irradiation of aqueous solutions of 1-methyl-2-phenyl-1-pyrrolinium perchlorate (1) in the presence of α-hydroxyalkanoate anions led to the formation of 2-(hydroxyalkyl)pyrrolidine adducts and a reduction product, 1-methyl-2-phenylpyrrolidine. Mechanistic studies demonstrated that photoaddition reactions were induced by one-electron transfers from the carboxylato groups of alkanoates to the excited singlet state of 1 (1S1), followed by an efficient decarboxylation. Furthermore, the photoreaction of 1 with ethoxyacetate was found to give a 2-(ethoxymethyl)pyrrolidine adduct in preference to the reduction product. For photoreactions with 2-mercaptopropionate and α-amino acids, the reduction product was detected. N-Acetylglycinate gave a 2-(acetylaminomethyl)pyrrolidine adduct in fairly high yield (80%). The features of these photoreactions with α-heteroatom-substituted alkanoates are discussed in terms of fluorescence-quenching efficiencies and the properties of radicals formed through electron transfers to 1S1.