Mechanistic studies on palladium-catalyzed double carbonylation of aryl iodides affording α-keto esters

Abstract

In relation to the mechanism of palladium-catalyzed carbonylation of aryl iodides to give α-keto esters, the carbonylation reactivity of some palladium complexes such as RPdIL 2 ( I: R = C 6H 5, L = P(C 6H 5) 3; II: R = C 6H 5CO, L = P(C 6H 5) 3) and C 6H 5COPd[P(C 6H 5) 3] 2(ClO 4)·acetone ( III) was investigated. In the carbonylation reaction in the presence of alcohols and t-amines, both complexes I and II exhibited the same reactivities. Complex II gave higher selectivities for α-keto esters when solvents of lower dielectric constant and lower donor number were used. The perchlorate complex III, which underwent double carbonylation with a high selectivity when treated with diethylamine and carbon monoxide, mainly gave simple esters in reactions with alcohols under carbon monoxide. The use of an alcohol in conjunction with a t-amine in the reaction of complex II could afford an α-keto ester, while the use of alkoxide resulted in exclusive formation of a simple ester. Heating of complex II with iodobenzene under carbon monoxide gave benzoyl iodide. These results are discussed in relation to the mechanism of catalytic double carbonylation.