HIGHLY REGIOSELECTIVE PALLADIUM-CATALYZED THIOCARBONYLATION OF ALLENES WITH THIOLS AND CARBON-MONOXIDE

A series of mono-and di-substituted allenes underwent direct thiocarbo nylation with thiols and carbon monoxide to form the corresponding bet a,gamma-unsaturated thioesters in 73-94% yields. This reaction require s 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) . CHC l3-PPh3, Pd(PPh3)(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 regioselectiv ity, in which the thiophenyl group adds to the less substituted double bond of allenes to give beta,gamma-unsaturated thioesters.