Novel photoreactions of chromene derivatives. The photolysis of 4-acetoxy-2h-chromene.

✍ Scribed by Maria J. Climent; Hermenegildo Garcia; Miguel A. Miranda; J. Primoa

• Book ID: 104205100
• Publisher: Elsevier Science
• Year: 1987
• Tongue: French
• Weight: 339 KB
• Volume: 43
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(01)90037-7

✦ Synopsis

The photolysis of 4-acetoxy-2H-chromene la 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 aKi-l=d arise from la 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 la.

This process and the [ 2+2 ] photodimerization are unprecedented in the photochemistry of ZH-chromenes.

Moreover, the photochemical epoxidation of la could have biological significance.