Thermal Rearrangement of Bicyclogermacrane-1,8-dione. Synthesis of Humulenedione and (-)-Cubenol, Starting from Natural (+)-Aromadendrene - V

Article abstract of DOI:10.1016/S0040-4020(01)85013-4

Treatment of a distillation tail of Eucalyptus globulus, containing mainly (+)-aromadendrene (1) and (-)-alloaromadendrene (2), with K/Al2O3 gives a quantitative conversion of 1 and 2 into isoledene (4).Oxidative cleavage of the central double bond in 4 produces (+)-bicyclogermacrane-1,8-dione (5).Thermal rearrangement of 5 gives via a homo <1,5> hydrogen shift at relatively low temperature the humulenedione 6, and at high temperature (FVP) the products 9 and 10 both with a cadinane skeleton.The naturally occurring humulenedione (7) and (-)-cubenol (17) can be synthesized starting from 6 and 9, respectively. - Key Words: sesquiterpene, flash vacuum pyrolysis, homo <1,5> hydrogen shift, humulane, cadinane