Crystal and molecular structure of carolenalone, a cycloheptenone sesquiterpene lactone from North Carolina Helenium autumnale L.

Abstract

X-Ray single crystal analysis has established the structure and relative stereochemistry of the title compound (I). Crystals are orthorhombic, space group P2₁2₁2₁, a= 7.31 (1), b= 21.20(1), c= 9.210 Å, Z= 4. The structure was solved by direct methods and atomic positional and thermal parameters were refined by full-matrix leastsquares calculations to R 0.078 over 476 reflections from diffractometer measurements. The cycloheptenone ring adopts a flattened twist-chair conformation in which the C:C·C:O system with a torsion angle of –157° is distinctly non-planar. The cyclopentane and γ-lactone rings are both in envelope conformations; the C(11) methyl group is β-oriented.