INTERMEDIATES IN THE PHOTOCYCLIZATION OF 1-(ORTHO-ALKYLPHENYL)PROPANE-1,2-DIONES

An intermediate in the photocyclisation of 1-(o-alkylphenyl)propane-1,2- diones may, in several cases, be efficiently trapped by sulphur dioxide but not by maleic anhydride. Reaction of 1-(o-bromoalkylphenyl)propane-1,2-diones with zinc leads to products expected from the photoenols of the parent diketones but there are significant differences between this reaction and the photocyclisation. It is argued that there is no evidence to implicate such enols as intermediates in the photoreaction.