The structurally rigid a-(o-alkylphenyl)acetophenone derivatives lacking b-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.