NOVEL PHOTOREACTIONS OF CHROMENE DERIVATIVES. THE PHOTOLYSIS OF 4-ACETOXY-2H-CHROMENE.

Article abstract of DOI:10.1016/S0040-4020(01)90037-7

The photolysis of 4-acetoxy-2H-chromene 1a leads to a mixture of o-acetoxyphenyl vinyl ketone 2a, 4-chromanone 3, chromone 4, 3-acetoxy-4-chromanone 5, 3-hydroxy-4-chromanone 6, and a cyclobutane dimer with anti head-to-head structure (7).The formation of 2a is explained by a photochemical electrocyclic opening of the pyran ring, followed by cis-trans photoisomerization and transacylation.Compounds 3 and 4 would arise from 1a by way of a photolytic cleavage of the acetyl-oxygen bond and subsequent disproportionation of the resulting radical 8.The isolation of the 3-substituted chromanones 5 and 6 can be accounted for in terms of a photochemical epoxidation of 1a.This process and the < 2+2 > photodimerization are unprecedented in the photochemistry of 2H-chromenes.Moreover, the photochemical epoxidation of 1a could have biological significance.