The first regioselective hydroformylation of acetylenic thiophenes catalyzed by a zwitterionic rhodium complex and triphenyl phosphite

The hydroformylation of acetylenic thiophenes is readily accomplished by using the zwitterionic rhodium catalyst (eta(6)-C6H5BPh3)-Rh+(1,5-COD) and triphenyl phosphite in the presence of CO and H-2. This catalytic system affords, as the major product, the alpha,beta-unsaturated aldehyde with the aldehyde and thiophene attached to the same olefin carbon atom. Assistance of sulfur from the heterocycle provides excellent regioselectivity and yields when the acetylenic unit is a propargyl ether or ester, phenylacetylene, or an enyne.