The epoxide configuration in palmarin, jateorin, and chasmanthin. X-ray analysis of a p-bromophenacyl ester of a palmarin derivative

Abstract

The epoxide ring in palmarin, jateorin, and chasmanthin is shown to be in the β-configuration by an X-ray analysis of a p-bromophenacyl ester of a palmarin derivative. The crystals are orthorhombic, space group P2₁2₁2₁, with four molecules of C₂₃H₂₃O₇Br in a unit cell of dimensions a= 10·76, b= 8·95, and c= 21·79 Å. The structure was solved by the heavy-atom method and refined by least-squares calculations. R is 0·078 for 1907 independent reflexions. The molecular framework of the derivative is highly distorted because of intramolecular overcrowding effects. A δ-lactone ring in the system is constrained to adopt a conformation with five of the ring atoms coplanar.