Photochemical Reactions. Photochemistry of Conjugated Methano-Epoxydienes: Participation of the Neighboring Cyclopropane Ring in Product Formation via Carbonyl Ylide and Carbene Intermediates

Article abstract of DOI:10.1002/hlca.19850680610

On singlet excitation (λ=254 nm, THF, pentane or hexane), the diastereoisomeric methano-epoxydines (E)-6 and (E)-7 undergo interconversion and yield the products 8-11.The main process is the cleavage of the oxiran ring to the vinyl carbene intermediate e which undergoes addition to the adjacent double bond furnishing the cyclopropene 8.The alternative carbene intermediate f is evidenced by the formation of the cyclobutene 10.For the fragmentation leading to 11, the carbene f as well as the dipolar species h are considered as possible intermediates.On triplet sensitization (aceton, λ>280 nm), (E)-7 shows behavior typical of epoxydienes, undergoing fission of the C-O bond of the oxirane ring and isomerization to the compounds 13, 14 and (E/Z)-15.