Dimerization reactions intramolecular diene coupling

By Intramolecular Heck Coupling. l-Bromo-1,5-dienes and 2-bromo-1,6-dienes cyclize in the presence of piperidine and a palladium acetate-tri-o-tolylphosphine catalyst to produce cy-clopentene derivatives (eq 39). 2-Bromo-l,7-octadiene, when subjected to the same reaction conditions, cyclized to yield a mixture of six and five-membered ring products, whereas competing dimerization and polymerization was observed for the more reactive 2-bromo-1,5 dienes. 

By the radical pathway l, -diesters, -diketones, -dienes or -dihalides, chiral intermediates for synthesis, pheromones and unusual hydrocarbons or fatty acids are accessible in one to few steps. The addition of the intermediate radicals to double bonds affords additive dimers, whereby four units can be coupled in one step. By way of intramolecular addition unsaturated carboxyhc acids can be converted into five raembered hetero- or carbocyclic compounds. These radical reactions are attractive for synthesis because they can tolerate polar functional groups without protection. 

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