Photochemical reaction of 3-hydroxy-1-(o-methylaryl)alkan-1-ones: formation of cyclopropane-1,2-diols and benzocyclobutenols through β- and γ-hydrogen abstractions

Abstract

Irradiation of 3-hydroxy-2,2-dimethyl-1-(o-methylaryl)-alkan-1-ones 1a–h having a bulky alkyl group or an aryl group on C-3 in methanol gave trans- and cis-cyclopropane-1,2-diols 2a–g and 3a, c–f, h and benzocyclobutenols 4a–h through β- and γ-hydrogen abstractions. Irradiation of 3-hydroxy-2,2-dimethyl-1-(o-methylphenyl)-alkan-1-ones 1i–k having ethyl, methyl or no substituent at C-3 gave benzocyclobutenols 4i–k and 1,3-diketones 5i, j, but no cyclopropane-1,2-diols. The cyclopropane-1,2-diols were sensitive to air and readily oxidized to the corresponding 1,3-diketones. Irradiation of 3-hydroxy-4,4-dimethyl-1-(o-methylaryl)pentan-1-ones 8a, b having a methyl group or no substituent on C-2 gave benzocyclobutenols 9a, b, the peroxide 10 and phthalides 11a, b. 3-Hydroxy-2,2-dimethyl-1,3-diphenylpropan-1-one 12a and 3-hydroxy-2,2,4-trimethylpentan-1-one 12b also underwent photocyclization through β-hydrogen abstraction to give cyclopropane-1,2-diols 13a, b and 14.