PHOTOCYCLOADDITION REACTIONS OF SOME 3-SUBSTITUTED CYCLOHEXENONES

The photochemical cyloaddition reactions of 3-methyl-, 3-phenyl-, and 3-acetoxycyclohexenones with the substrates cyclopentene, isobutene, 1,1-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]octan-2-ones in which the orientation of the substituents is, in most cases, that predicted by the Corey rule of the oriented π complex. Irradiation of 3-acetoxy-and 3-methylcyclohexenone with isobutylene yielded, in addition, significant quantities of the 8,8-dimethylbicyclo[4.2.0]octan-2-one derivatives, indicating that steric factors can sometimes outweight mild electronic demands in a substrate. The relative rates of addition of the various enones to each substrate were determined. These vary over one order of magnitude and are suggestive of processes involving diradical-like intermediates with a low degree of charge separation. © 1969, American Chemical Society. All rights reserved.