Modhephene: a sesquiterpenoid carbocyclic [3.3.3]propellane. X-Ray crystal structure of the corresponding diol

Cameroonane, Prenopsane and Nopsane, Three New Tricyclic Sesquiterpene Skeletons

“…The 1 H-NMR spectrum (C 6 D 6 ) again revealed three methyl singlets (δ ϭ 0.97, 1.04, 1.30), a methyl doublet (δ ϭ 1.03), and an isolated methylene group (δ ϭ 1.56, 1.75, J AB ϭ 14 Hz). Spin decoupling and HMBC experiments gave the same fragments as those mentioned above for prenopsanol (17). However, in contrast to the alcohol 17 the HMBC spectrum showed a 3 J correlation of 7-H (δ ϭ 2.06) with C-2 (δ ϭ 32.2) and with C-3 (δ ϭ 31.4).…”

“…Recently, we reported on the constituents of this oil (see Table 1 and Scheme 1). [3] However, the structure of the three sesquiterpene alcohols (15,17,18), and the configuration of the four diastereomers of silphiperfolan-6-ol (19Ϫ22), remained unknown. We have now elucidated the structures of these compounds and, additionally, those of two other (new) sesquiterpenes; the alcohol 23 and the diene 24.…”

“…lelyi C. D. Adams (Compositae) contains only sesquiterpenes, which are mainly triquinanes. Besides the known tricyclic compounds, silphiperfol-5-(1, 3) and -6-ene (4), modhephen-2-ene (5), α-(6) and β-isocomene (7), silphiperfolan-7β-ol (12), presilphiperfolan-8-ol (13), silphiperfol-6-en-5-one (14) and 7-epi-silphiperfolan-6β-ol (20), the following compounds, three of which (15,17,18) have new skeletons, were found, for the first time, occurring naturally: presilphiperfol-7-ene (2), cameroonan-7-ol (15), an 11(7Ǟ8)-abeoEchinops giganteus var. lelyi C. D. Adams (Compositae) is an endemic species of Cameroon and Nigeria.…”

“…The 1,3-hydride shift ("b") of the silphinane cation D gives the intermediate F which was formulated by Zalkow [17] as precursor of the isocomane cation H (Ǟ 6, 7) and the modhephane cation I (Ǟ 5, 23). As described by Coates [21] two 1,2-shifts ("a") of the silphinane cation D afford the terrecyclane cation G, but derivatives of this cation G could not be identified in the Echinops oil.…”

Rearrangements of tricyclic ketones: [3.3.3]propellane formation via a γ-enolate revealed in an approach to the pentalenene skeleton through β-enolization

“…Pentalenene is the biosynthetic precursor of the pentalenolactones (4), antibiotic metabolites produced by several Streptomyces species, and it has been synthesized by several groups through a variety of routes (1,5). Isocomene cooccurs with the first carbocyclic propellane to be found in nature, modhephene (3) (6). Several syntheses of these fascinating structures have been described: isocomene ( l , 7 ) and modhephene (8).…”