A new general procedure for the Heck arylation of disubstituted olefins is described. This procedure allows, in many instances, the stereoselective synthesis of trisubstituted olefins. Trisubstituted olefins are easily accessible under mild reaction conditions using a new catalyst system consisting of dicyclohexylamine or methyl-(dicyclohexyl)amine and a phase-transfer catalyst. The choice of base was found to be crucial for the rate and stereoselectivity of the Heck arylation reactions. This method is applicable to the coupling of both electron-deficient and electron-rich aryl halides and displays good stereoselectivity and a high degree: of functional group compatibility. Labeling studies indicate that the source of this selectivity is thermodynamic in nature.