Longifolene
Longifolene is the common chemical name of a naturally occurring, oily liquid hydrocarbon found primarily in the high-boiling fraction of certain pine resins. The name is derived from that of a pine species from which the compound was isolated, Pinus longifolia
Chemically, longifolene is a tricyclic sesquiterpene. This molecule is chiral, and the enantiomer commonly found in pines and other higher plants exhibits a positive optical rotation of +42.73°. The other enantiomer is found in small amounts in certain fungi and liverworts.
Longifolene is used in organic synthesis for the preparation of dilongifolylborane, a chiral hydroborating agent.
Longifolene is also one of two most abundant aroma constituents of lapsang souchong tea, because the tea is smoked over pinewood fires.
Total syntheses
Due to the compact tricyclic structure and lack of functional groups, Longifolene is an attractive target for research groups highlighting new synthetic methodologies. Notable syntheses are by Corey, McMurry, Johnson, Oppolzer, and Schultz. Fallis has published a stereoselective synthesis of -longifolene using an intramolecular Diels-Alder strategy.| Longifolene total synthesis by Corey.svg |
The Johnson biosynthesis has since been validated as feasible using modern quantum mechanical computational methods. The subsequent cationic cascade mechanism has been shown to go through a non-classical cation intermediate.