Overcoming challenges in the palladium-catalyzed synthesis of electron deficient ortho-substituted aryl acetonitriles

Abstract

Highly electron deficient monoaryl, di-aryl and bis-diaryl acetonitriles were effectively synthesized using either a nucleophilic aromatic substitution (NAS) or a palladium-mediated coupling pathway. Synthesis of di-aryl acetonitriles most conveniently proceeded via NAS--palladium-mediated coupling was not required. This reaction, however, results in a product that is more acidic than the reactants. Facile deprotonation of the product prevents efficient formation of the bis-diaryl acetonitrile through a NAS pathway. Thus, palladium-mediated coupling is required to prepare the bis-diaryl acetonitrile efficiently. In the palladium-catalyzed coupling, choice of base and solvent (and thus the counter cation for the benzylic anion nucleophile) is important. Also, choice of the supporting ligand is important, indicating the sensitivity of the reaction to steric and ligand electronic effects.