PALLADIUM(0)-CATALYZED ALKOXYCARBONYLATION OF ALLYL PHOSPHATES AND ACETATES

Palladium-catalyzed alkoxycarbonylation of allyl phosphates under CO (1 atm) at 50-degrees-C proceeds highly efficiently to give the corresponding beta,gamma-unsaturated esters. The carbonylation of geranyl phosphate ((E)-11) under CO (1 atm) at 50-degrees-C gave ethyl ester of homogeranic acid ((E)-12) stereoselectively. The carbonylation takes place at the least substituted allylic positions with inversion of configuration. Typically, the methoxycarbonylation of cis-5-(methoxycarbonyl)-2-cyclohexen-1-yl phosphate (cis-16) gave trans-dimethyl 2-cyclohexene-1,5-dicarboxylate (trans-17) selectively. Alkoxycarbonylation of allyl acetates is performed for the first time in the presence of a catalytic amount of bromide ion. The reaction can be rationalized by assuming the mechanism which involves oxidative addition of palladium(0) species to allyl acetates to give pi-allylpalladium acetate, fast ligand exchange of the acetate with bromide, insertion of carbon monoxide to give acylpalladium species, and alkoxylation.