Photodecarboxylation of Arylacetic Acids.

Arylacetic acids, when the carboxyl group is at a secondary or tertiary carbon, are decarboxylated in considerable yields on irradiation of their aqueous alkaline solutions with 254 nm light, while the corresponding free acids are not decarboxylated. Together with the simple decarboxylation reaction (type A), two other side reactions, oxidative decarboxylation (type B) and decarboxylative dimerization (type C), were observed for some compounds, particularly when >290 nm light was used. The observation of high-yield decarboxylation of angularly substituted phenanthridone derivatives suggests that the above photodecarboxylation reaction would be a useful synthetic tool, if the substrate is appropriately designed.