First examples of enantioselective palladium-catalyzed thiocarbonylation of prochiral 1,3-conjugated dienes with thiols and carbon monoxide: Efficient synthesis of optically active beta,gamma-unsaturated thiol esters

A catalyst system based on [Pd(OAc)(2)]/(R,R)-DIOP has been found to effect asymmetric thiocarbonylation of certain prochiral 1,3-dienes to produce go od yields of optically enriched,beta,gamma -unsaturated thiol esters. The r eaction was performed under an atmosphere of carbon monoxide (400 psi) at 1 10 degreesC in methylene chloride for 60 h. The asymmetric thiocarbonylatio n proceeded with good to excellent enanotioselectivities (up to 89% ee). Th e stereoselectivity is strongly influenced by the structure of the chiral p hosphine ligands and substrates, as well as by the reaction conditions. The enantiodetermination step is assumed to be CO insertion to a pi -allylpall adium intermediate.