Nickel-catalyzed oligomerization of functionalized conjugated dienes

The cyclodimerization of several functionalized dienes with nickel(0) catalysts has been studied. When a functional group, such as a methoxycarbonyl or a trimethylsiloxy group, is bonded directly to the terminal carbon of the diene grouping, a completely regio- and stereo-selective dimerization is observed and trans -1,2-disubstituted cycloocta-3,7-dienes are formed in good yields (80–90%). When one carbon atom separates the functional group from the diene group, the yield drops significantly (to 30%), and the stereoselectivity and the clean nature of the reaction are completely lost. The effect of the nature of the nickel catalyst and the influence of the reductive organoaluminum species are discussed. The particular structure and the stereochemical features of the cyclooctadiene derivatives allow a better understanding of the various steps involved in the catalytic process. A reaction mechanism is proposed.