Photoreactions in clay media: singlet oxygen oxidation of electron-rich substrates mediated by clay-bound dyes

Photooxidation of electron-rich substrates such as quinol, 1-naphthol and anthracene to the corresponding 1,4-quinones with clay-bound methylene blue/rose bengal is studied in acetonitrile medium under oxygen atmosphere. A [4+2] cycloaddition between singlet oxygen and the substrate, followed by its subsequent cleavage is the predominant reaction with clay-supported sensitisers. With anthracene, while [4+2] cycloaddition is the favoured pathway, a minor reaction involving electron-transfer is also likely.