Photooxidation of Hantzsch 1,4-dihydropyridines by molecular oxygen

Photooxidation of Hantzsch 1,4-dihydropyridines (1,4-DHP, 1a–1d) by direct irradiation (λ > 300 nm) under an oxygen atmosphere has been carefully examined in this work. Spectroscopic and electrochemical studies demonstrate that photoinduced singlet electron transfer from 1,4-DHP to molecular oxygen occurs. The generated superoxide radical anion (O₂^–•) is responsible for this typical photochemical oxidation.