Palladium-Catalyzed Coupling Reaction of α-Diazocarbonyl Compounds with Aromatic Boronic Acids or Halides

Efficient palladium-catalyzed cross-coupling reactions of alpha-diazocarbonyl compounds and arylboronic acids or aryl halides have been developed. The reaction proceeds smoothly for a range of diazo compounds, boronic acids, and halides. The coupling reaction conditions tolerate various substituents on the aromatic rings of the substrates, such as chloro, fluoro, acyl, oxo, ester, and nitro groups. This coupling reaction constitutes a novel access to alpha-aryl-substituted alpha,beta-unsaturated carbonyl compounds. Mechanistically, palladium-carbene is supposed to be the key intermediate; its formation is followed by migratory insertion of an aryl group to the carbenic carbon of the palladium-carbene complex and subsequent beta-hydride elimination. Kinetic isotope effect (KIE) data measured for intra- and intermolecular competition experiments suggest that beta-hydride elimination is not involved in the rate-determining step.