Ein neues sesquiterpenketon aus Arnica-arten

Enantio- and Diastereocontrolled Synthesis of an Angular Triquinane Sesquiterpene (+)-Arnicenone

“…The latter afforded the former on reflux in dichloromethane in the presence of p -toluenesulfonic acid. Spectroscopic data of (+)-arnicenone 1 thus obtained were identical with those reported for the natural product . Thus, the absolute configuration was determined as 1 R ,3a R ,5a S ,8a R by correlation with the configuration of the starting chiral building block (−)- 2 .…”

“…We have recently developed an efficient route to the α-hydroxymethylketone 2 serving as a synthetic equivalent of chiral 2-hydroxymethylcyclopentadienone by employing either an enzymatic or a catalytic procedure. Utilizing this chiral building block, which exhibits inherent convex-face selectivity, we attempted diastereoselective construction of (+)-arnicenone 1 , an isocomene-type angular triquinane sesquiterpene isolated from the essential oil of rhizomes and roots of Arnica plants, to determine the absolute configuration of this natural product unambiguously as well as to develop a general enantio- and diastereocontrolled route to the isocomene-type sesquiterpenes. We report here the first diastereocontrolled synthesis of (+)-arnicenone 1 from (−)- 2 which allowed determination of the absolute configuration of the natural product unambiguously as 1 R ,3a R ,5a S ,8a R (Scheme ).…”

Carbocationic Rearrangements of Silphinane Derivatives

“…A similiar scheme was postulated independently by Hanson in connection with studies on botrydial biosynthesis . The structures of presilphiperfolan-8-ol ( 23 ) 6c,, and the recently discovered 9-ol isomer 8f,15 corresponding to hydration of ions 8 and 7 , respectively, provided support for this hypotheses. The results of isotope labeling experiments 16 on the biosynthesis of botrydial 17 afford experimental evidence in accord with this scheme and in particular demonstrate the occurrence of an 8,9 hydride shift 16b in the formation of the presumed presilphiperfolan-8-ol intermediate ( 23 ).…”

“…The isolation and structure elucidation of isocomene ( 1 , Chart ) and modhephene ( 2 ) 1b,− by L. Zalkow, F. Bohlmann, and associates heralded the subsequent discovery of not only numerous analogues and oxidized metabolites − but also several different skeletal types of tricyclopentanoid sesquiterpenes, including the silphiperfolene isomers (e.g. 3 ) 4,8 and silphinene ( 4 ). ,5b,, These novel structures raise interesting questions concerning the biogenetic origins and relationships of these natural products .…”

Triquinanes and Related Sesquiterpenes Revisited Computationally: Structure Corrections of Hirsutanols B and D, Hirsutenol E, Cucumin B, Antrodins C–E, Chondroterpenes A and H, Chondrosterins C and E, Dichrocephone A, and Pethybrene

“…Generally, inter- or intramolecular hydrogen bonds may notably perturb the carbonyls’ chemical shifts. Luckily these effects are mostly localized on the carbonyl carbons and do not propagate into the rest of the molecule. …”