ON THE TWOFOLD HECK REACTION OF 4-VINYLCYCLOHEXENE AND P-DIHALOBENZENES

The palladium-catalyzed reaction of iodobenzene, p-haloiodobenzenes (p -C(6)H(4)IX'; X'=F, Cl, Br, I) and p-dibromobenzene with 4-vinylcycloh exene (Heck arylation reaction of olefins) was investigated with Pd(OA c)(2)/PR(3)/Et(3)N (R=phenyl, o-tolyl) as a classical catalyst system and with Pd(OAc)(2)/KOAc/[BzEt(3)N]Cl in DMF as a phase-transfer catal yst system, respectively. Iodobenzene reacts with 4-vinylcyclohexene t o give (E)-2-(cyclohex-3-enyl)vinylbenzene (1) as main product. p-Halo iodobenzenes react with 4-vinylcyclohexene to give (E)-p-halo-2-(cyclo hex-3-enyl)vinylbenzene (3), p-halo-1-(cyclehex-3-enyl)vinylbenzene (4 ) or (E,E)-p-bis[2-(cyclohex-3-enyl)vinyl]benzene (5) depending on the reaction conditions and the catalyst system used. The phase-transfer catalyst system is less reactive but more selective. A reaction temper ature of 80 degrees C is necessary for reaction with p-dibromobenzene. The investigations demonstrate the much higher reactivity of the exoc yclic double bond of 4-vinylcyclohexene in comparison with the endocyc lic one.