Terminal alkyne dicarbonylation can be readily effected under mild conditions b y treating alkynes with carbon monoxide and alcohols or water at 25-80°C in the presence of Pdlp, KI and air, with unprecedented catalytic efficiency. Dicarbonylated products are mainly maleic esters or acids and their ring-chain tautomers. The latter are formed to a large extent at room temperature. Reaction pathways are discussed.Dicarbonylation of alkynes with carbon monoxide has been known for several years,' but even the most recent literature reports methods which are not completely satisfactory particularly from the standpoint of catalytic efficiency. However, alkyl-or aryl-maleic esters and acids are interesting products, which can be used as monomers for polymerization, so an efficient procedure to prepare these compounds is a useful target. We now report such a procedure, which affords high yields of alkyl-or aryl-maleic esters and acids under mild conditions. A preliminary account, limited to prop-2-ynyl alcohol, was published r e c e n t l ~. ~

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The unique properties of I(-) allow it to be involved in several different ways in reactions catalyzed by the late transition metals: in the oxidative addition, the migration, and the coupling/reductive elimination steps, as well as in substrate activation. Most steps are accelerated by I(-)(for example through an increased nucleophilicity of the metal center), but some are retarded, because a coordination site is blocked. The "soft" iodide ligand binds more strongly to soft metals (low oxidation state, electron rich, and polarizable) such as the later and heavier transition metals, than do the other halides, or N- and O-centered ligands. Hence in a catalytic cycle that includes the metal in a formally low oxidation state there will be less tendency for the metal to precipitate (and be removed from the cycle) in the presence of I(-) than most other ligands. Iodide is a good nucleophile and is also easily and reversibly oxidized to I(2). In addition, I(-) can play key roles in purely organic reactions that occur as part of a catalytic cycle. Thus to understand the function of iodide requires careful analysis, since two or sometimes more effects occur in different steps of one single cycle. Each of these topics is illustrated with examples of the influence of iodide from homogeneous catalytic reactions in the literature: methanol carbonylation to acetic acid and related reactions; CO hydrogenation; imine hydrogenation; and C-C and C-N coupling reactions. General features are summarised in the Conclusions.

[reaction: see text] 2-Oxazolidinones 2 are obtained in excellent yields (up to 100%) and with unprecedented catalytic efficiencies (up to 2000 mol of product/mol of catalyst used) by direct PdI2/KI-catalyzed oxidative carbonylation of the readily available 2-amino-1-alkanols 1. Reactions are carried out in MeOH as the solvent at 100 degrees C using a 1/6/5 CO/O2/air mixture (60 atm total pressure at 25 degrees C).

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N-Alkylprop-Zynylamines readily react with carbon dioxide in the presence of catalytic amounts of strong organic bases and undergo intramolecular cyclization to 5-methylene-1.3-oxazolidin-2-ones in good yields.

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 60−80 °C in the presence of catalytic amounts of PdI2 in conjunction with KI and under a 4:1:10 mixture of CO/air/CO2 (60 atm total pressure at 25 °C). 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)