Sesquiterpenoids. Part XVIII. X-Ray crystallographic determination of the stereochemistry and conformation of miscandenin, an elemanediolide with a dihydro-oxepin ring

Abstract

The stereochemistry of miscandenin, a sesquiterpene elemanediolide, has been determined by X-ray crystalstructure analysis. The dihydro-oxepin and cyclohexane rings are cis-fused; the former adopts a twist-boat conformation and shows appreciable angular strain, while the latter has a distorted chair conformation. The α,γ-fused γ-lactone at C(4)–(6) adopts a slightly distorted half-chair conformation whereas the β,γ-fused γ-lactone at C(7)–(8) is closer to an envelope form in which C(7) is the out-of-plane atom. Crystals are orthorhombic, a= 8·586(4), b= 14·918(5), c= 10·211(3)Å, Z= 4, space group P2₁2₁2₁. The structure was solved by direct methods from diffractometer data and the atomic parameters were adjusted by least-squares calculations which converged to R 7·0% over 1222 reflections.