Valence photoisomerization of 2H-pyrans

Conclusions 2H-Pyrans under the influence of UV light undergo reversible cleavage of the C-O bond and are isomerized to the corresponding dienones, for which reversible photochemical cis-trans isomerization around the C=C bond is characteristic, and not photochemical cyclization to 2H-pyrans.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 390–394, February, 1981.The authors express their deep gratitude to V. A. Kuz'min for a valuable discussion of the study results.