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

Abstract
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.

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