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Competitive Formation of Ylide and Carbene Intermediates from 1 π,π*‐Excited α,β‐Unsaturated γ,δ‐Epoxyketones
Author(s) -
Bischofberger Norbert,
Frei Bruno,
Wirz Jakob
Publication year - 1983
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.19830660814
Subject(s) - chemistry , ylide , carbene , excited state , photochemistry , absorption (acoustics) , medicinal chemistry , organic chemistry , atomic physics , catalysis , physics , acoustics
Laser flash photolyses (λ = 265mm) of the γ,λ‐epoxyenones 1–3, 7 and 8 , the α,β‐unsaturated γ,δ‐epoxy ester 6 , and the epoxytriene 9 at ambient temperature produced short‐lived transients with broad absorption maxima in the visible region, which are identified as carbonyl ylides. Comparison of the rather long‐wavelength absorption maxima with the results of standard PPP SCF SCI calculations suggests that some degree of twisting is present in all the ylides studied. The lifetimes of the order of hundreds of ns of these intermediates and Stern ‐ Volmer analysis of the trapping of the carbonyl ylide derived from 2 with CH 3 COOH provide conclusive evidence that the carbene products are not formed via the carbonyl‐ylide intermediate (Scheme 3) .