Stereochemistry of 1,6-germacradien-5-ol, a constituent of the needles of Scots pine (Pinus sylvestris) and of the defence secretion from larvae of the pine sawfly Neodiprion sertifer

(-)-1,6-Germacradien-5-ol [(E, E) -1, 5-dimethyl-8-isopropylcyclodeca-1,6-d ien-5-ol, I] has been isolated from the defence secretion from larvae of th e pine sawfly Neodiprion sertifer and from needles of Scots pine (Pinus syl vestris). It was characterised by means of spectroscopic methods and by its optical rotation. Acid-promoted transannular cyclisation isomerised 1 to t he known (-)-alpha-cadinol. (4), whereby the configuration at position 8 wa s established as S. The configuration at the second stereocentre, position 5, carrying the alcohol group is discussed on the basis of molecular mechan ics calculations (MM2), NMR shift values, coupling constants and NOESY expe riments. 1-endo-Bourbonanol (7a) and (-)-5-methoxy-1,6-germacradiene (8) we re prepared from 1 and investigated by NMR spectroscopy. The evidence colle cted indicated that the stereoisomer isolated was (5S,8S)-1,6-germacradien- 5-ol.