Zur Kenntnis der katalytischen Dimerisation von Acrylsäurederivaten mit Hilfe von Palladium‐Komplexen. III. Reaktionen von β‐Palladioacrylestern und deren Beziehung zur Katalytischen Reaktion

On the Knowledge of the Catalytic Dimerization of Acrylic Acid Derivatives by Palladium Complexes. III Reactions of β‐Palladio Acrylates and Their Relation to the Catalytic Reaction Complexes of the type L2PdCl(CH  CHCOOCH3) (L2 = 2 PPh3 or Ph2PCH2CH2PPh2) were decomposed to dimethyl muconate by pyrolysis or by substraction of the phosphine ligands with (CH3CN)2PdCl2 in acetonitrile. The last mentioned reaction gave Δ3‐dimethyl dihydromuconate in the presence of hydrochloric acid. Δ3‐Dimethyl dihydromuconate was also formed by decomposition of (Ph2PCH2CH2PPh2) PdCl (CH  CHCOOCH3) with HBF4 in acetonitrile, but the analogous reaction in methyl acrylate as solvent gave Δ2‐dimethyl dihydromuconate. Thus, we have simulated the formation of the two main products of the catalytic dimerization of methyl acrylate with palladium(II)chloride in a stoichiometric manner. Mechanisms with hydride and carbene intermediates are discussed.