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Photochemische Reaktionen 115. Mitteilung [1]. Zur Photochemie konjugierter γ,δ‐Epoxyenone: Der Einfluss eines Hydroxylsubstituenten in ϵ‐Stellung
Author(s) -
Nakamura Norio,
Schweizer Wolfhard Berned,
Frei Bruno,
Wolf Hans Richard,
Jeger Oskar
Publication year - 1980
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.19800630813
Subject(s) - chemistry , allene , bicyclic molecule , substituent , stereochemistry , bond cleavage , double bond , triclinic crystal system , ylide , medicinal chemistry , crystal structure , crystallography , organic chemistry , catalysis
Photochemistry of Conjugated γ,δ‐Epoxyenones: The Influence of a Hydroxy Substituent in ϵ‐Position On 1 n, π*‐ or 1 π,π*‐excitation (λ ≥ 347 or λ=254 nm), the ϵ‐hydroxy‐γ;,δ‐epoxyenone 8 undergoes fission of the C(γ)O bond followed by the cleavage of the C(δ)‐C(ϵ) bond. This hitherto unknown sequence of reactions is evidenced by the structure determination of the new type products 10–17 and 25 , including a synthetic proof for 12 and the X‐ray analysis of 11 (X‐ray data: triclinic P 1; a =7,386(2), b =8,904(4), c =9,684(5)Å; α=82,29(4)°, β=74,46(3)°, γ=82,29(3)°; Z =2). The selective 1 π,π*‐excitation also induces competitive C(γ)‐C(δ) bond cleavage to yield the bicyclic acetal 18 and a ketonium‐ylide intermediate a , which photochemically forms a carbene b giving the allene 19 and the cyclopropene 20 . On 1 n,π*‐excitation of the acetate 9 the initial C(γ)‐O bond fission is, in contrast to the behaviour of the corresponding alcohol 8 , followed by a 1,2‐methyl shift affording ( E/Z )‐ 28 or by a cyclization‐autoxidation process yielding the lactone 29 .