Atmospheric Pressure Carbonylation of Allylic Compounds

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The palladium-catalyzed carbonylation of allylic compounds offers a synthetic method of alpha, beta-unsaturated acid. However, the carbonylation has found less application, because it requires a high carbon monoxide pressure. Several years ago we have found that the atmospheric pressure carbonylation proceeds smoothly at room temperature in the presence of strong bases such as or It was necessary to add sodium alkoxide slowly and dropwise to the allylic halides, to avoid an excess of the bases.In the present study we aimed at simplifying the reaction procedure and the catalyst system and optimizing the reaction using cinnamyl chloride as the substrate. As the catalyst of the biphasic reaction of aq. NaOH/organic solvent pDCl_2p[ph_2p(m-C_6H_4SO_3Na)]_2 gave the best results in terms of yield and rate of CO uptake. We considered a possibility that the facile carbonylation involved the CO insertion into a pd-O bond, rather than a pd-C bond. It seemed likely that this process occurs in the aqueous phase.In the carbonylation of the homogeneous CH_3ONa/CH_3OH system, Na_2PdCl_<4'> without any phosphorus ligand, gave methyl esters in high yields. On the other hand, palladium complexes with phosphorus ligand gave methyl ethers as the major product. The presence of the phosphorus ligand affects the carbonylations significantly.More work is needed to define the pathway of this carbonylation.