The structure and absolute configuration of (−)‐β‐Sesquiphellandrene ((−)‐1a) is shown to be (6S)‐2‐methyl‐6‐[(1′R)‐4‐methylidenecyclohex‐2‐enyl]hept‐2‐ene by stereospecific synthesis of its enantiomer ((+)‐1a) and of a further (6S,1′S)‐diastereoisomer ((+)‐1b). Characteristic spectroscopic differences in both diastereoisomeric series are discussed.
Das bislang unbekannte rac-Homofenchon (2) lafit sich ausgehend vom Cyclohexencarbonslureester 4 uber das Bicyclo[3.2.l]octen 13 auf zwei unabhangigen Wegen gewinnen. Schliisselschritte stellen dabei wahlweise entweder die mit Trifluoressigsaureanhydrid induzierte innermolekulare Acylierung einer C = C-Bindung in 9 dar, oder die BF,-katalysierte Zersetzung des Diazomethylketons 15. Von 13 fuhrt ein direkter Weg zum Homofenchon (2). dessen Kernresonanz-Spektren vollstAndig zugeordnet wur.den.
First Synthesis of rac-Homofenchone (1,4,4-TrimethylbicycloI3.2.l]octan-3-one)The rac-homofenchone (2), which was previously unknown, is prepared starting from the cyclohexenecarboxylate 4 ilia the bicyclo[3.2. lloctene 13 by two independent routes. The key steps are either the intramolecular acylation of a C = C bond in 9 induced by trifluoroacetic acid anhydride, or the BF3-catalyzed decomposition of the diazomethyl ketone 15. From 13 a direct path leads to homofenchone (2), the NMR spectra of which were fully assigned.
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