Structure and absolute stereochemistry of the sesquiterpene alcohol (–)-myliol: X-ray analysis of the p-bromobenzoate

Abstract

The structure and absolute configuration of the novel sesquiterpene alcohol, (–)-myliol (C₁₅H₂₂O) have been determined by X-ray analysis of its p-bromobenzoate (III). Crystals of the p-bromobenzoate (III) are triclinic, space group P1, a= 10.37(1), b= 10.20(1), c= 10.39(1)Å, α= 107.8(1), β= 71.6(1), γ= 110.3(1)°, Z= 2, with two independent molecules in an asymmetric unit. The structure was solved by the heavy-atom method, and refined by block-diagonal least-squares to R 0.085 over the 1 956 independent observed reflections. The absolute configuration was determined by the anomalous dispersion effect. The two molecules in the asymmetric unit have similar geometries, and each contains a novel fused 5,3,6,3-tetracyclic ring system. The two cyclopropane rings in this fused ring are in conjugation and the central cyclopropane ring conjugates further with an exo-double bond. The cyclopentane ring in this skeleton has an envelope conformation and the cyclohexane ring is considerably distorted by the two fused cyclopropane rings.