Stereochemical assignment by X-ray crystallography to the product of trapping by solvent of the intermediate zwitterion on irradiation of a 2,5-cyclohexadienone

Ultraviolet irradiation of 4-methyl-4-trichloromethylcyclohexa-2,5-dienone in acidic methanol resulted in the stereospecific generation of a solvent adduct, whose structure has been determined by X-ray crystallography, and whose carbon skeleton can be identified with that of the previously postulated zwitterion intermediate. It is concluded that the photochemical rearrangement of this dienone to the corresponding lumiketone proceeds with inversion of configuration at the migratory carbon.