Palladium-Catalyzed Double-Carbonylation of Alkenyl Halides with Secondary Amines To Give α-Keto Amides

Abstract The double-carbonylation reaction of alkenyl halides with diethylamine in the presence of palladium catalysts has been examined in detail. The reaction gives α-keto amide together with amide, the single-carbonylation by-product. The yield of α-keto amide is strongly dependent on the nature of alkenyl halide. Alkenyl bromides or iodides having phenyl group(s) as substituent(s) on the vinyl group are successfully double-carbonylated under appropriate reaction conditions and the corresponding α-keto amides are obtained in good to modest yields together with amides. In contrast, the reactions of alkenyl halides without a phenyl group give amides exclusively. In order to clarify the reason for the substrate-specificity in the reaction, series of alkenyl- and alkenoylpalladium(II) complexes, the presumed intermediates in the catalytic reactions, have been prepared and their reactions with secondary amines, carbon monoxide, and alkenyl halides were examined. The study suggests the operation of three types of processes for amide formation in the catalytic reactions. Possible mechanisms for amide as well as α-keto amide formation are discussed.