RHODIUM-CATALYZED CARBONYLATION OF ACETYLENES UNDER WATER-GAS SHIFT REACTION CONDITIONS - SELECTIVE SYNTHESIS OF FURAN-2(5H)-ONES

Rhodium-catalyzed carbonylation of acetylenes was studied. Under water-gas shift reaction conditions, internal acetylenes are selectively carbonylated to 3,4-disubstituted furan-2(5H)-ones (2). Use of D2O gave 5,5-dideuteriofuran-2(5H)-one (3), which indicates that the hydrogen comes from water. Use of molecular hydrogen in place of water gave hydroxymethylated product 4 and stilbene 5, and no furanone was obtained, indicating that water-gas shift reaction conditions are indespensable for the formation of furanones. As catalysts, rhodium carbonyl clusters such as Rh4(CO)12 and Rh6(CO)16 are the best among the transition-metal complexes tested. The presence of amines is essential for the selective synthesis of furanones. Effects of additives, solvents, and the pressure of carbon monoxide were examined.