Cope rearrangement of some germacrane-type furan sesquiterpenes. Part V. Preparation and thermal rearrangement of some cis,trans-germacranolides

Abstract

The cis,trans-germacranolides (3Z,9E)-8-acetoxy-6-hydroxygermacra-3,9-dien-12-oic acid γ-lactone (VIIIa) and its deacetoxy-derivative (VIIIb) were synthesized by sensitized photoisomerization of their 3E,9E-isomers [dihydrolaurenobiolide (VIIa) and its deacetoxy-derivative (VIIc)]. Cope rearrangements of (VIIIa and b) and the related alcohols (3Z,9E)-germacra-3,9-diene-6,8,12-triol (IXa) and (3Z,9E)-germacra-3,9-diene-6,12-diol (IXb) established that the presence of a fused five-membered ring at positions 6 and 7 in the cis,trans-cyclodecadiene derivatives has an important effect on the rearrangement. The c.d. spectra of these and some reference compounds indicate that the stereochemistry of the Cope-rearrangement products can be deduced from the signs of the c.d. couplet of the cyclodecadiene.