10.1246/cl.1980.131
The research investigates the photochemical substitution of ring hydrogen in pyridinecarboxylic esters by alkyl groups derived from solvent alcohols, aiming to elucidate the multiple pathways involved in this process. The study found that the photoalkylation of pyridinecarboxylic esters occurs via several paths, including alkylation initiated by the excited carbonyl moiety of the ester group and alkylation initiated by the excitation of the π-electronic system of the pyridine ring. Methyl 2-pyridinecarboxylate (1) and methyl 3-pyridinecarboxylate (5) are key compounds used to investigate the photochemical substitution of ring hydrogen by alkyl groups derived from solvent alcohols. Methyl 2-pyridinecarboxylate is used to study the dependence of photoalkylation on the added acid, revealing that alkylation occurs at different positions depending on the presence of acid. In the absence of acid, alkylation occurs at the β-position, while in the presence of sulfuric acid, alkylation occurs exclusively at the γ-position. Methyl 3-pyridinecarboxylate is used to explore the complex acidity dependence of photoalkylation and photoalkoxylation, showing that these processes compete under certain conditions. The study also examines the effects of different solvents (methanol and ethanol) and additives (such as benzene, naphthalene, and anthracene) on the photoreactions, revealing that alkylation and alkoxylation originate from different excited states. The results highlight the roles of these compounds in demonstrating the multiple pathways and complex mechanisms involved in the photoalkylation of pyridinecarboxylic esters.
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