NEW INSIGHTS INTO THE PALLADIUM-CATALYZED SYNTHESIS OF DELTA-LACTONES FROM 1,3-DIENES AND CARBON-DIOXIDE

Two-coordinate Pd(0) complexes are shown to be important intermediates in the telomerization of 1,3-dienes and CO2 using palladium/phosphine catalysts without additives, Only one phosphorus atom is bound to palladium during the C-C bond forming steps, but the second phosphorus atom is crucial in the early stages of the catalytic cycle and for the elimination of the product, A ligand that gave an active palladium catalyst for the coupling of 1,3-butadiene and CO2 has been designed, Use of a palladium catalyst in the reaction of isoprene with CO2 allowed for the first time isolation and NMR spectroscopic characterization of the resulting mixture of lactones.