Structure and absolute configuration of fraxinellone: X-ray analysis of 9β-bromofraxinellone

Abstract

X-Ray crystal-structure analysis of 9β-bromofraxinellone has defined the absolute stereochemistry of fraxinellone. The crystals are monoclinic, space group P2₁, with two molecules of the bromo-derivative in a unit cell of dimensions a= 9·98, b= 8·00, c= 9·73 Å, β= 119·3°. Atomic co-ordinates were determined by Fourier and least-squares calculations, the final R value over 1023 independent reflexions being 0·117. The absolute configuration is in accord with the theory that fraxinellone is a degraded limonoid. The molecule contains a cyclohexene ring in an envelope-like conformation; the γ-lactone ring is intermediate between a half-chair form and an envelope form.