Abstract
The structures of a new skeletal type of sesquiterpene lactone, containing a seven, five, fivering system, and of its putative precursor, a 9-oxo-melampolide, have been confirmed by single crystal X-ray structure determination. The central 5-membered ring of the new skeleton istrans-fused to the cycloheptene ring andcis-fused to the lactone ring. Transannular interactions and the geometry of thetrans carbon-carbon double bond of the oxo-melampolide and the keto-group at C9, suggest that the new seven, five, five tricyclic skeleton-type of montahibisciolide can easily be reached by a transannular cyclization process. The isobutyrloxy group of the oxo-melampolide is disordered into two partially populated conformations. 8α-(2′-Methylbutyryloxy)-9α-hydroxymontahibisciolide,3, C20H28O5, crystallizes in orthorhombic space groupP212121 witha=8.294(2),b=9.740(2),c=22.675(1) Å,V=1832(1)Å3,Z=4. The structure was refined toR=0.043 andR w=0.048 for 2898 observed reflections with CuKα radiation. 8α-isobutyryloxy-9-oxo-germacra-4E, 1(10)Z-dien-6β, 12-olide,4, C19H24O5, crystallizes in monoclinic space groupC2 witha=32.879(7),b=5.793(2),c=9.884(4)Å, β=99.01(3)°,V=1859.5(9)å3,Z=4. The structure was refined toR=0.054 andR w=0.064 for 1010 observed reflections with MoKα radiation.
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Quijano, L., Rios, T., Toscano, R.A. et al. Structures of 8α-(2′-methylbutyryloxy)-9α-hydroxymontahibisciolide, a new skeletal type of sesquiterpene lactone, and of its precursor 8α-isobutyryloxy-9-oxo-germacra-4E, 1(10)Z-dien-6β,12-olide. J Chem Crystallogr 26, 753–757 (1996). https://doi.org/10.1007/BF01664652
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DOI: https://doi.org/10.1007/BF01664652