Multiple Paths for Photo-alkylation and -alkoxylation of 3-Pyridinecarboxylic Ester in Alcohol. Simultaneous Contribution of Several Kinds of Excited States

Article abstract of DOI:10.1246/bcsj.54.1761

UV-irradiation of methyl 3-pyridinecarboxylate (1) in acidic alcoholic solutions brings about the alkoxylation and alkylation at the pyridine ring.Photoalkylation occurs in several paths: 1) alkylation initiated by the triplet ?-?^* state, 2) alkylation initiated by the triplet n-?^* state of the carbonyl moiety of the ester group, 3) alkylation initiated by exciplex between a free base form of 1 and a pyridinium form of 1, and 4) alkylation promoted by chloride ions.Photoalkoxylation originates from a singlet excited state of 1.In the photoreactions of 1 in strongly a cidic methanolic solutions acidified with H2SO4, three kinds of excited states (two kinds of triplet states for alkylation and a singlet state for alkoxylation) contribute simultaneously.