Convenient, Rapid and Highly Regioselective Cycloisomerisation of 4,4-Disubstituted Hepta-1,6-Dienes Employing Neutral Palladium Chloride pro-Catalysts

Optimum conditions for the cycloisomerisation of dimethyldiallylmalonate by complexes of the form [L2PdCl2] (L = RCN or DMSO) were found to be [(t-BuCN)2PdCl2] in 1,2-dichloroethane at 40 °C. These conditions also allow the highly regioselective cycloisomerisation of a range of 4-substituted hepta-1,6-dienes to the corresponding 1-substituted 3,4-dimethylcyclopent-2-enes in good yield. However, substituents at the 4 position that are strongly coordinating inhibit the reaction.