Stereochemical features of the structure of germacrane lactones and the applicability of Geissman's rule in this series

Stereochemical features of the structure of the germacrane lactones have been investigated. By correlating the circular dichroism and the results of x-ray structural analyses of the germacranolides with different types of linkage of the lactone ring it has been estabished that Geissman's rule is satisfied in the trans-trans-germacral(10), 4-dienolide series if the lactone ring has the S-conformation and the decadiene ring the chair-chair conformation in the C₆-trans-lactones and, correspondingly, the A and chair-chair conformations in the C₆-cis compounds. The decadiene ring has the boat-boat conformation if there is an exocyclic double bond at C₁₀ in the C₈-trans-germacrolides, and a positive Cotton effect (CE) is observed in the CD spectra in the 220 nm region and a negative one at 200 nm.Institute of Chemistry of Plant Substances Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 742–748, November–December, 1990.