Photochemical Reactions of Aromatic 1,3-Diketones having a Functional Group on beta-carbon in the Side Chain.

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Photochemical reactions of ortho-methyl, -ethyl, and -isopropylaryl ketones having a functional group such as carbonyl, hydroxyl, alkoxyl, or acetoxy group on beta-carbon in their side chain have been investigated. The chemical behavior of the photoproducts have also been investigated.Irradiation of ortho-alkylarylketones with a beta-keto or beta-ester group gave the corresponding benzocyclobutenols in good yields. The pyrolysis of the benzocyclobutenols thus obtained gave benzocyclobutenones.Ortho-alkylarylketones with a beta-hydroxyl or beta-alkoxyl group underwent photocyclization via beta- or gamma-hydrogen abstraction to give benzocyclobutenols and cyclopropane-1,2-diols or 2-alkoxyclopropanols.Irradiation of ortho-alkylarylketones with a beta-hydroxyl or beta-acetoxy group gave two diastereomeric benzocyclobutenols, which underwent thermal interconversion.The acid treatment of benzocyclobutenols formed from ortho-alkylarylketones with a beta-hydroxyl or beta-acetoxy group and two methyl groups on alpha-carbon gave isopropylidenebenzocyclobutenes.Irradiation of ortho-isopropylarylketones with a hydroxyl group on beta-carbon gave 2,2-dimethylbenzocyclobutenols which underwent stereospecific hydrogen shift from C-2 methyl group to C-1 carbon on thermal conditions to give arylalcohols with ortho-isopropylidene group.1- (2', 4', 6'-Trialkylphenyl) -2-methyl-1,3-diketones exists in the enol from in solution. The reaction of singlet oxygen with these enolic 1,3-diketones were affected by solvent polarity, and proceeded through two different conformational isomeric perepoxide.