SYNTHESIS BASED ON CYCLOHEXADIENES .15. TOTAL SYNTHESIS OF (+ -)-PREZIZAENE, (+/-)-PREZIZANOL AND (+/-)-JINKOHOL-II/

A new methodology for the synthesis of the complex ring system tricycl o[6.2.1.0(1.5)]undecane. present in the zizaene group of sesquiterpene s, is described. Acid-catalysed rearrangement of the endo alcohol 20 a fforded the enone 12, which was transformed stereoselectively into the key intermediate. (+/-)-norprezizanone 10. The features of the synthe sis are the transformation of a bicycle[2.2.2] octane framework into a bicycle[3.2.1] octane system by an acid-catalysed rearrangement and a stereoselective conjugate addition of a methyl group on an alpha,beta -unsaturated keto ester at -100 degrees C. Norprezizanone was converte d into the sesquiterpenes (+/-)-prezizanol 5 and(+/-)-prezizaene 4. Th e first total synthesis of (+/-)-jinkohol II 6 is also presented.