HIGHLY REGIOSELECTIVE THIOCARBONYLATION OF ALLYLIC ALCOHOLS WITH THIOLS AND CARBON-MONOXIDE CATALYZED BY PALLADIUM COMPLEXES - A NEW AND EFFICIENT ROUTE TO BETA,GAMMA-UNSATURATED THIOESTERS

The reaction of allylic alcohols with thiols and carbon monoxide in th e presence of catalytic quantities of Pd(OAc)(2) (3 mol %), triphenylp hosphine (12 mol %), and p-TsOH (5 mol %) leads to a novel thiocarbony lation to afford beta,gamma-unsaturated thioesters in good to excellen t yields. Other palladium catalyst systems such as Pd-2(dba)(3). CHCl3 -PPh3-p-TsOH, Pd(PPh3)(4)-p-TsOH, and Pd(OAc)(2)-dppb-p-TsOH are also effective for this transformation. The thiocarbonylation reaction is b elieved to proceed via a allylpalladium intermediate. The reaction occ urs highly regioselectively at the least hindered allylic terminal car bon of the substrate to give the products. This new carbonylation proc edure was readily applied to a variety of allylic alcohols and both ar omatic and aliphatic thiols.