The photochemical cyloaddition reactions of &methyl-, 3-phenyl-, and 3- acetoxycyclohexenones with the substrates cyclopentene, isobutene, l, l-dimethoxyethylene, ethoxyethylene, cis-and trans-dichloroethylene, and acrylonitrile have been studied. These enones add to the various substrates bearing electron-donating substituents to give, sometimes accompanied by other products, bicyclo [4.2. 0] octsn-2-ones in which the ...