Telomerization of Piperylene

3 Pentadiene (piperylene) is, like isoprene, a major component in the C5-cut of naphtha pyrolysis. It can be expected that in the near future the Cs-cut will be used more extensively by the chemical industry and that a greater number of C5-separation plants will be built. In this case 1,3-pentadiene could become a useful starting material for technical synthesis. 

Also piperylene can be used in telomerization however, so far only poor yields have been obtained [35]. Therefore, our investigations were focused on finding reactive nucleophiles and active catalyst systems which allow the telomerization of piperylene in high yields and selectivities [36]. We found that the three alcohols benzyl alcohol, furfuryl alcohol and 2,2,2-trifluoroethanol proved to be very reactive nucleophiles in the telomerization of piperylene. 

It can be assumed that the electron-withdrawing effect of the aromatic, the furanoic and the fluorine-containing substituents influences the polarity of the OH-bond, thus facihtating the attack of the alcohol. 

Besides smaller amounts of 1 1-adducts of piperylene and alcohol, the head-tail-linked telomer 2-alkoxy-6-methyl-3y8-nonadiene was formed in good selectivities (Equation 30). 

The most favourable catalyst proved to be an in situ system of palladium-bis(acetylacetonate) modified by a phosphorus ligand. With regard to the benzyl alcohol, best results ( 60% yield of telomer) have been obtained with 1,1,1-trimethylolpropanephosphite, a ligand of low basicity and of low steric hindrance. A difficulty with the phosphite ligands consists in the fact that their coordination to the metal is low and that they do not stabilize the palladium sufficiently at higher reaction temperatures. To avoid the precipitation of palladium metal, temperatures lower than 60 are favourable. 

---