Highly Regioselective Palladium-Catalyzed Thiocarbonylation of Allenes with Thiols and Carbon Monoxide

A series of mono- and di-substituted allenes underwent direct thiocarbonylation with thiols and carbon monoxide to form the corresponding beta,gamma-unsaturated thioesters in 73-94% yields. This reaction requires catalytic quantities of Pd(OAc)(2) (3 mol %) and triphenylphosphine (12 mol %) in THF under an atmosphere of CO (400 psi) at 100 degrees C for 48 h. Other palladium catalyst systems such as Pd(2)(dba)(3).CHCl(3)-PPh(3), Pd(PPh(3))(4), and Pd(OAc)(2)-dppp are also effective for this reaction. The thiocarbonylation reaction is believed to proceed via an allylpalladium intermediate. The reaction exhibits high regioselectivity, in which the thiophenyl group adds to the less substituted double bond of allenes to give beta,gamma-unsaturated thioesters.