Efficient heterolytic photodecarboxylation of 6-coumarinylacetic acids

A series of four 6-coumarinylacetic acids (1–4) was prepared and their photochemistry was investigated in neutral aqueous solution. All four derivatives undergo photodecarboxylation (PDC) under these conditions with very high efficiency (Φ = 0.50–0.83) to give arylmethyl products consistent with a mechanism involving carbanion reaction intermediates. Quenching studies indicate that PDC occurs from both singlet and triplet states. This work demonstrates that the coumarin chromophore is sufficiently electron-withdrawing in the excited state to promote carbanion-forming reactions.