Photolysis of 4-acetoxychromene adsorbed onto an Fe3+ - exchanged sepiolite

Photolysis of 4-acetoxy-2H-chromene (1) adsorbed onto an Fe3+-modified sepiolite gives rise to chromanone (5) (38%), 3-acetoxy-4-chromanone (6) (26%) and cyclobutane dimer (7) (11%), in sharp contrast with the reported homogeneous liquid phase irradiation. On the basis of the results obtained from the photolysis of 1 sensitized by 2,4,6-triphenylpyrylium tetrafluoroborate and the detection of the perylene radical cation in samples of perylene adsorbed on the same sepiolite, it is proposed that the reaction mechanism involves single-electron transfer between the excited state of 1 and the Fe3+ site in the clay.