Photochemical reaction of 1-(o-methylphenyl)-2,2-dimethyl 1,3-diketones

The photochemistry of 1-(o-methylphenyl)-2,2-dimethylpropane-1,3-diones 4 has been investigated. Compounds 4a–h underwent photocyclization to give benzocyclobutenols 11a–h and naphthalenones 12a–h in hexane or methanol. Compound 4i gave the naphthalenone 12i in methanol. The product ratio 11:12 was greater in hexane than in methanol. This ratio increases with chain branching of the C-3 substituent R and with increasing size of R. Compounds 4a, b and d gave isobutyrophenones 13a, b and d along with products 11 and 12 in hexane.