Photochemistry of 2,6‐dimethyl‐4‐pyrone in trifluoroethanol

Photolysis of 2,6‐dimethyl‐4‐pyrone ( 1 ) in trifluoroethanol gave, in addition to the previously observed dimer 2 , three volatile primary photoproducts 3, 4 , and 5. Continued irradiation led to the disappearance of the three volatile products with formation of 6. This secondary photo‐product was shown to arise from 3 and 4 while 5 was converted to non‐volatile products. The formation of 3, 4 , and 5 can be viewed as arising from an oxybicyclohexenyl zwitterion formed by electrocyclic ring closure of 1. This zwitterion can thus be trapped by solvent to yield 3 and 4 or rearrange to 5 via and epoxycyclopentenone intermediate. The conversion of 3 and 4 to 6 is explained in terms of a Norrish type II process.