Photoisomerisation reactions of cyclohepta-2,4-dienone and 2-methylcyclohepta-2,4-dienone

In non-polar solvents cyclohepta-2,4-dienone and 2-methylcyclohepta-2,4-dienone give upon irradiation the corresponding bicyclo[3,2,0]hepta-6-en-2-ones, where as in polar acidic solvents, including FSO3H, norbornen-7-ones are formed.