COMBINED OXIDATIVE AND REDUCTIVE CARBONYLATION OF TERMINAL ALKYNES WITH PALLADIUM IODIDE-THIOUREA CATALYSTS

Oxidative carbonylation of alkynes can be carried out catalytically in the absence of added oxidants if it is coupled with a reductive carbo nylation process at the expense of the same alkyne involved in the oxi dative process. Maleic esters (from oxidative carbonylation) and unsat urated lactones (from reductive carbonylation) are the main products f ormed under the catalytic action of palladium iodide complexes with th iourea (tu). A complex, formally corresponding to the ionic formula [P dI(tu)(3)]I, allows the reaction of alkylacetylenes at room temperatur e and atmospheric pressure. With activated alkynes such as phenylacety lene, or with alkynes containing coordinating groups, other palladium complexes with two or four molecules of thiourea are also active, alth ough to a lesser extent. Identification of the organic by-products giv es a hint of the mechanism by which coupling of oxidative and reductiv e carbonylation occurs.