Synthesis of maleic anhydrides and maleic acids by Pd-catalyzed oxidative dicarbonylation of alk-1-ynes

We have found that carbon dioxide effectively promotes the Pd-catalyzed oxidative carbonylation of terminal alkynes to give maleic anhydrides in fair yields. Reactions were carried out in aqueous dioxane at 60-80degreesC in the presence of catalytic amounts of PdI2 in conjunction with KI and under a 4.1.10 mixture of CO/air/CO2, 160 atm total pressure at 25degreesC. By working in the presence of a large excess of water, maleic acids were formed selectively with unprecedented catalytic efficiencies for this kind of reaction. In the latter case, the use of an excess of carbon dioxide tended to inhibit, rather than promote, the reaction. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).