Most 2, 4-~ yclohexadienones undergo reversible ring fission on irradiation to form ketenes which may be trapped by suitable nucleophiles.'~ 2~ 2a On the other hand certain alkyl- substituted dienones undergo specific photoisomerization to bicyclo [3. lO] hexenones to the complete exclusion of ring-opened products, even with alcohols as solvent. An important controlling factor in these processes is the pattern of substitution in the dienone, and it has ...
