Journal of Photoscience (2002), Vol. 9(1), pp. 13−15Photoinduced Enolization of 2-(Ortho-tolyl)benzofuran-3-one†

The structurally rigid α-(o-alkylphenyl)acetophenone derivatives lacking β-hydrogens, 3,3-dimethyl-2-o-tolylibdan-1-one and 2-o-tolyl-benzofuran-3-one, were prepared and their photochemical behaviors were examined. The former did not give any photoproduct while the latter turned into its enol tautomer. The difference of reactivity of two ketones was attributed to aromatic character of the enol of the benzofuranone. It was concluded that the reaction occurred via photoinduced 1,3-H transfer. key words: enolization, benzofuranone If there are several reaction pathways possible from a given molecule, selectivity in product distribution can be decided by various factors. Such behaviors can be found not only in ground state chemistry but also in excited state chemistry. We have recently shown such an example in the photochemistry of α-(o-tolyl)acetophenone and its derivatives [1-3]. Without α-substituents, α-(o-alkylphenyl) acetophenones shows efficient photocyclization via 1,5-biradicals formed by hydrogen atom abstraction of carbonyl groups [4]. Putting an alkyl(or aryl