Elusive Alkynylation Achieved

Adding an alkyne handle to an already decorated organic molecule gives synthetic chemists the opportunity to create even more elaborate structures. Although there are several options for adding alkynes to organic compounds, examples of tacking carbon-carbon triple bonds onto molecules in place of C–H bonds when the carbon is an sp³-hybridized center are rare. Aiming to expand this area of chemistry, Jin-Quan Yu and colleagues at Scripps Research Institute, in California, developed a palladium-catalyzed alkynylation of the β-carbon in aliphatic amides, shown (J. Am. Chem. Soc., DOI: 10.1021/ja400648w). The reaction makes use of a Pd(0) catalyst bearing an N-heterocyclic carbene or a phosphine ligand and tolerates a wide range of functional groups. Yu’s team used the system to alkynylate more than a dozen different amides, including some containing ethers and trifluoromethyl groups. Mechanistic studies indicate the reaction involves a Pd(0)-catalyzed C−H activation step and does not need external oxidant to close the catalytic cycle. This last feature could improve the sustainability and practicality of C−H activation reactions. The group plans to do an enantioselective version of the alkynylation reaction using chiral ligands.