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Über Dienketene aus o ‐Chinolacetaten
Author(s) -
Quinkert Gerhard,
Kleiner Erna,
Freitag BerndJürgen,
Glenneberg Jürgen,
Billhardt UtaMaria,
Cech Franz,
Schmieder Klaus R.,
Schudok Clemens,
Steinmetzer HansChristian,
Bats Jan W.,
Zimmermann Gottfried,
Dürner Gerd,
Rehm Dieter,
Paulus Erich F.
Publication year - 1986
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.19860690302
Subject(s) - chemistry , nucleophile , adduct , conformational isomerism , bicyclic molecule , population , photochemistry , medicinal chemistry , bond cleavage , nuclear magnetic resonance spectroscopy , stereochemistry , organic chemistry , molecule , catalysis , demography , sociology
On Dien‐Ketenes from o ‐Quinol‐Acetates A detailed picture of the photochemistry of o ‐quinol‐acetates is presented. (RS)‐ 6‐Acetoxy‐6‐methyl‐ , (RS)‐ 6‐acetoxy‐2,6‐dimethyl‐ , (RS)‐ 6‐acetoxy‐5,6‐dimethyl‐ , (RS)‐ 6‐acetoxy‐2,4,6‐trimethyl‐ , (RS)‐ 6‐acetoxy‐2,3,4,6‐tetramethyl‐ , and (RS)‐ 6‐acetoxy‐2,3,4,5,6‐pentamethyl‐2,4‐cyclohexadien‐1‐ones serve as representative educts. There are two separate main photochemical routes conveniently designated as 1 (π*, n) or 3 (π*, π) tracks. The latter may also be attained by sensitization and leads to phenols. The former, by α‐cleavage furnishes dienketens as indispensable phototransients. Photolysis of dien‐ketens follows one or more of three reaction channels, each of which yields a particular type of photoproduct: heat‐induced monocyclization affords 2,4‐cyclohexadien‐1‐ones, heat‐induced bicyclization stereoselectively furnishes bicyclo[3.1.0]hex‐3‐en‐2‐ones, and multi‐step addition of protic nucleophiles stereoselectively gives 1,4‐, 1,6‐ and/or 1,2‐adducts. By X‐ray analysis or NOE studies, the structure of isolated photoproducts is established. Conventional spectroscopy at low or flash spectroscopy at normal temperature yield information on the formation and decay of kinetically unstable intermediates. Photoproduct composition depends on the pattern of substitution of the educts, on the solvents, and on the nucleophiles that might be present. Substituents primarily exert an influence upon the population of the various conformers of the dien‐keten. Solvents affect the rate of the divers reaction paths competing for the phototransient. Nucleophiles play more than a trivial role when adducts are formed. With the detailed view of a dien‐keten's role on hand, the photoproduct from a given o ‐quinol‐acetate or more general from a linear conjugated cyclohexadienone is now predictable.