1H 13C NMR and X-ray crystallographic studies of highly polyhalogenated derivatives of costunolide lactone

The costunolide lactone, a sesquiterpene compound isolated from Zaluzania triiloba species, reacted with several dihalocarbene sources produced by trihaloform-NaOH under successive phase transfer reactions yielding mono-, bis- and tris-dihatocyclopropane adducts. The structures, as well as the configurational assignments of the different derivatives, were established by H-1 and C-13 NMR spectroscopy and assisted by X-ray crystal lographic and molecular modelling studies. The specific shielding of protons in the neighbourhood of different halogens on the cyclopropane moieties was correlated to the pseudocontact interactions. (c) 2005 Elsevier B.V. All rights reserved.