Metals in organic syntheses XII. Hydrocarboalkoxylation of ethyl 3-butenoate catalyzed by palladium complexes

The effects of the main reaction parameters on yield and regioselectivity in the hydrocarboalkoxylation of ethyl 3-butenoate, catalyzed by a [PdCl2(PPh3)2]-PPh3 system, have been investigated. A higher regioselectivity towards diethyl glutarate is obtained in a polar solvent, such as ethanol, or in the presence of higher concentrations of added PPh3 or under low carbon monoxide pressure. As a general trend, higher regioselectivity is obtained at the expense of the yield. In ethanol, high yields but low regioselectivities are obtained when the catalyst is employed together with HCl; in benzene the presence of HCl strongly inhibits the catalysis. In the presence of molecular hydrogen no hydroformylation occurs, the yield is much higher and the regioselectivity remains practically the same; moreover, the inhibitory effect of HCl is suppressed. The palladium catalyst is highly active and regioselective in the presence of SnCl2.