The structure and conformation of umbellifolide, a 4,5-secoeudesmane derivative

Synthesis of 4,5‐seco‐eudesman‐type sesquiterpenes: 4,5‐dioxo‐10‐epi‐4,5‐seco‐γ‐eudesmane and 4,5‐dioxo‐10‐epi‐4,5‐seco‐γ‐eudesmanol

“…Synthesis was commenced with the commercially available (+)-dihydrocarvone (3). Compound 4 was easily prepared in 85% yield with >95% diastereomeric excess (deduced from 1 H NMR) by refluxing the mixture of methyl acrylate, anhydrous K 2 CO 3 , and compound 3 in tert-butanol for 12 h. The stereochemistry of methyl group was determined as a by NOESY due to axial attack of methyl acrylate in the stable conformation of the enolate of the ketone 3.…”

Reassignment of NMR spectra and conformational study of the sesquiterpene lactone goyazensolide

“…19 Germacranes lactonized at C-8 are conformationally more mobile than those cyclized at C-6. 20,21 The minimum energy structures determined by molecular mechanics calculations displayed the same conformation for the cyclodecane ring. The differences between the conformers lay in the orientation of the side-chains, especially the hydroxymethyl group at C-4 for which a rotation barrier of about 2 kcal mol 1 has been calculated.…”

Anionic and Photochemical Behaviour of the Medium‐Sized Terpenoid Ketone 8‐Dehydro‐12‐O‐methyl‐deacylhallerin

“…Ketone 2 emerged as a suitable substrate because of its availability in multigram amounts by modification of the natural product hallerin (1) [8,10] and the presence of the reactive 1,4-diene system. Enolization of 2 with LDA at -80°C and subsequent protonation resulted in the recovery of the starting material, presumably as the product of enolization at the less substituted C-9 carbon atom and formation of a dienolate that was reprotonated without any rearrangement (Scheme 1).…”

“…[3,4] Much less is known about the anionic rearrangements of this type of compounds, [5] as well as about their photochemical behaviour. [6,7] To complement previous studies on the cationic rearrangements of medium-sized terpenoids, [8,[9][10][11] we have now investigated the behaviour of the enone 2 toward bases and light, supporting the experimental results with X-ray crystal structure data and theoretical molecular dynamics (MD) and quantum chemical calculations.…”