Sesquiterpenes from Juniperus thurifera L. Stereochemistry in Unusual Cedrane and Duprezianane Series

The analysis of the essential oil from the wood of Juniperus thurifera has provided the isolation of seven new natural products, including the first described examples of 2-epi-cedranes and 2-epi-duprezianane. The co-occurrence in the oil of the three cedrane-type arrangements (cedrane, 1,7-diepi-cedrane and 2-epi-cedrane) has permitted, after a thorough 2D NMR analysis the unequivocal spectroscopical assignment of each of the three cedrane skeletons, and subsequently the development of an unambiguous method for establishing their stereochemistries. A useful pattern for distinguishing between the two duprezianane stereochemistries is also given.