Vibrational Circular Dichroism (VCD), VCD Exciton Coupling, and X-ray Determination of the Absolute Configuration of an [alpha],[beta]-Unsaturated Germacranolide

The absolute configuration of 1 was deduced by vibrational circular dichroism together with the evaluation of the Flack and Hooft X-ray parameters. Vibrational circular dichroism exciton coupling, using the carbonyl group signals, confirmed the absolute configuration of 2. In addition, sodium borohydride reduction of the 11,13-double bond of 6-epi-desacetyllaurenobiolide (1) yields an almost equimolecular mixture of C11 epimers, while reduction of the same double bond of 6-epi-laurenobiolide (2) provided almost exclusively the (11S) diastereoisomer 4. Chirality 27:247-252, 2015. © 2015 Wiley Periodicals, Inc.