Methyl Esters as Cross-Coupling Electrophiles: Direct Synthesis of Amide Bonds

Abstract

Amide bond formation and transition metal-catalyzed cross-coupling are two of the most frequently used chemical reactions in organic synthesis. Recently, an overlap between these two reaction families was identified when Pd and Ni catalysts were demonstrated to cleave the strong C–O bond present in esters via oxidative addition. When simple methyl and ethyl esters are used, this transformation provides a powerful alternative to classical amide bond formations, which commonly feature stoichiometric activating agents. Thus far, few redox-active catalysts have been demonstrated to activate the C(acyl)–O bond of alkyl esters, which makes it difficult to perform informed screening when a challenging reaction needs optimization. We demonstrate that Ni catalysts bearing diverse NHC, phosphine, and nitrogen-containing ligands can all be used to activate methyl esters and enable their use in direct amide bond formation.