polysubstituted 2,6-cycloheptadien-1-ones gave bicyclo[3.2.0]hept-3-en-2-ones, lumiketone-like products, which subsequently photoisomerized to bicyclo[2.2.1]hept-2-en-7-ones. The reaction of cycloheptadienones to lumiketones was proven to proceed via a triplet excited state from both sensitization and quenching experiments.