5, 5-Dimethylcyclohexane-1, 3-dione and its derivatives were shown to isomerize to give 5, 6-dihydropyran-4-ones on irradiation in FSO3H or 98% H2SO4. The 2, 2-dimethyl derivative, lacking hydrogen on C2, failed to give any products under the same conditions. A similar type of isomerization was also observed with thiolane-2, 4-dione and its derivatives, while no photoisomerization was observed with their nitrogen or oxygen analogs. A possible ...
