X-Ray structure of a fluoroguaianolide derivative

Abstract

The molecular structure of a fluoro-derivative (IV) of a guaianolide has been established by single-crystal X-ray diffraction techniques. The compound is a product of the BF₃-catalyzed opening of an epoxide group in a 1,10-epoxyguaianolide (III) derived from the germacranolide sesquiterpene lactone dihydroparthenolide (I). Crystals of (IV) are orthorhombic, space group P2₁2₁2₁, with Z= 4 in a unit cell of dimensions a= 8.975(2), b= 11.174(2), c= 14.583(6)Å. The structure was refined to R 0.027 for 1 648 reflections. The molecule features a fullysaturated cis-fused guaianolide-type skeleton with idealized symmetry C_s, having the seven-membered ring in the chair and the five-membered ring in the envelope conformation. Substituents on this fused ring system are α-F at C(1), α-OH and β-Me at C(4), an α-methyl-γ-lactone trans-fused at C(6) and C(7), and α-Me and β-OH substituents at C(10). The stereochemistry of the precursor 1,10-epoxide is thus inferred to be β.