Longifolene is the common (or trivial) 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 (obsolete name for Pinus roxburghii Sarg.)
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 (optical rotation -42.73°) 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.
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.
^Corey, E. J.; Ohno, Masaji.; Mitra, Rajat B.; Vatakencherry, Paul A. (February 1964). "Total Synthesis of Longifolene". Journal of the American Chemical Society. 86 (3): 478-485. doi:10.1021/ja01057a039.
^Corey, E. J.; Ohno, Masaji; Vatakencherry, Paul A.; Mitra, Rajat B. (March 1961). "TOTAL SYNTHESIS OF d,l-LONGIFOLENE". Journal of the American Chemical Society. 83 (5): 1251-1253. doi:10.1021/ja01466a056.
^McMurry, John E.; Isser, Stephen J. (October 1972). "Total synthesis of longifolene". Journal of the American Chemical Society. 94 (20): 7132-7137. doi:10.1021/ja00775a044.
^Volkmann, Robert A.; Andrews, Glenn C.; Johnson, William S. (August 1975). "Novel synthesis of longifolene". Journal of the American Chemical Society. 97 (16): 4777-4779. doi:10.1021/ja00849a062.
^Oppolzer, Wolfgang; Godel, Thierry (April 1978). "A new and efficient total synthesis of (.+-.)-longifolene". Journal of the American Chemical Society. 100 (8): 2583-2584. doi:10.1021/ja00476a071.
^Schultz, Arthur G.; Puig, Salvador (March 1985). "The intramolecular diene-carbene cycloaddition equivalence and an enantioselective Birch reduction-alkylation by the chiral auxiliary approach. Total synthesis of (.+-.)- and (-)-longifolene". The Journal of Organic Chemistry. 50 (6): 915-916. doi:10.1021/jo00206a049.
^Bo, Lei; Fallis, Alex G. (May 1990). "Direct total synthesis of (+)-longifolene via an intramolecular Diels-Alder strategy". Journal of the American Chemical Society. 112 (11): 4609-4610. doi:10.1021/ja00167a105.