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 (η 6 -C 6 H 5 BPh 3 ) - Rh + (1,5-COD) and triphenyl phosphite in the presence of CO and H 2 . This catalytic system affords, as the major product, the α,β-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.