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Photochemical reactions. 146 th communication . Photochemistry of conjugated methano‐epoxydienes: Participation of the neighboring cyclopropane ring in product formation via carbonyl ylide and carbene intermediates
Author(s) -
Bischofberger Norbert,
Frei Bruno,
Jeger Oskar
Publication year - 1985
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19850680610
Subject(s) - chemistry , carbene , photochemistry , cyclopropene , cyclopropane , isomerization , ylide , dichlorocarbene , cyclobutene , allene , singlet state , allylic rearrangement , ring (chemistry) , medicinal chemistry , excited state , organic chemistry , catalysis , physics , nuclear physics
On singlet excitation (λ = 254 nm, THF, pentane or hexane), the diastereoisomeric methano‐epoxydienes ( E )‐ 6 and ( E )‐ 7 undergo interconversion and yield the products 8 – 11 . The main process is the cleavage of the oxirane 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 (acetone, λ > 280 nm), ( E )‐ 7 shows behavior typical of epoxydienes, undergoing fission of the CO bond of the oxirane ring and isomerization to the compounds 13 , 14 and ( E / Z )‐ 15 .