(E, E)-, (E, Z)- and (Z, Z)-diallylic sulfones (6) undergo stereospecific Ramberg-Backlund reaction to give (E, E, E)-, (E, E, Z) - and (Z, E, Z)-1, 3, 5-hexatrienes (7), respectively, upon treatment with CBr~2F~2 in the presence of alumina-supported KOH. The stereoselectivity of the reaction depends on the solvent and temperature. Good (E)-selectivity (>95%) can usually be obtained by conducting the reaction at 0℃ in CH~2Cl~2 but in some circumstances better (E)-stereoselectivity can be achieved when the reaction is performed at -78℃ in V(t-BuOH):V(CBr~2F~2)=1:1 mixture. The can be achieved when the reaction is performed at -78℃ in V(t-BuOH):V (CBr~2F~2)=1:1 mixture. The stereoselective syntheses of galbanolenes (7m) and (7n) using this newly developed method are exemplified.

Key words: STEREOSELECTIVITY, SULFONE, HEXATRIENE