Xyloccensin E

The title compound (also known as phragmalin triacetate), C35H42O14, is a phragmalin-type limonoid extracted from X. rumphii. The mol­ecule consists of eight rings with the orthoacetate group bridged at positions 1, 8 and 9. The two five-carbocyclic rings (A 1 and A 2) and the dioxolane ring (G) adopt a distorted envelope conformation. The 1,3-dioxane ring (E) exists in a chair conformation. The six-carbocyclic rings (B and C) exhibit a twisted-boat conformation. The lactone ring has a half-chair conformation and the furan ring is planar (r.m.s. deviation = 0.002 Å). Rings A 1/B, A 2/B, B/C, C/D and C/G are all cis-fused. The two acet­oxy groups attached to ring B and the furan ring attached to the lactone ring are in equatorial positions. The porous crystal packing exhibits voids of 688 Å3 and weak inter­molecular C—H⋯O inter­actions. The absolute configuration was assigned on the basis of literature data

7-Deacetyl­gedunin

The title compound [systematic name: (1S,3aS,4aR,4bS,5R,6aR,10aR,10bR,12aS)-1-(furan-3-yl)-5-hy­droxy-4b,7,7,10a,12a-penta­methyl-4b,5,6,6a,7,10a,10b,11,12,12a-deca­hydro­naphtho­[2,1-f]oxireno[2,3-d]isochromene-3,8(1H,3aH)-dione], C26H32O6, which is a limonoid-type triterpene isolated from the seeds of X. moluccensis, crystallizes with three independent mol­ecules with very similar geometries in the asymmetric unit. In each mol­ecule, the four fused six-membered rings of the genudin core adopt distorted half-chair, chair, twist-boat and twisted half-chair conformations. In the crystal, inter­molecular O—H⋯O hydrogen bonds link the mol­ecules into helical chains propagated in [100]. Weak non-classical C—H⋯O contacts further consolidate the crystal packing

Towards novel difluorinated sugar mimetrics; syntheses and conformational analyses of highly-functionalised difluorinated cyclooctenones

Highly-functionalised difluorinated cyclooctenones were synthesised from trifluoroethanol using either metallated difluoroenol acetal or carbamate chemistry, followed by a [2,3]-Wittig rearrangement or aldol reaction. Efficient RCM reactions afforded the title compounds which showed rather restricted fluxional behaviour by VT 19F NMR. Topological characterisation by molecular modelling and NOESY/ROESY experiments offered a number of challenges, but allowed the identification of two favoured boat-chair conformers which interconverted by pseudorotation with relatively large activation barriers