Generation of 10-Diazolongibornane from Longifolene and Synthesis of Neolongifolene-the Elusive Progenitor of Isolongifolene

Neolongifolene 2, the elusive progenitor of isolongifolene 3, has been synthesised from longifolene in five steps. The strategy consists in generating the crucial longibornyl-10-cation 11 under basic conditions (via 10-diazolongibornane 9 in a protic Bamford-Stevens reaction), which then expels a proton after prior rearrangement, thus affording the target olefin 2; on exposure to any acid, 2 readily collapses into isolongifolene 3.