Development of Dipicolinic Acid Based Mono-Amides as New Ligands for Copper Catalyzed Carbon-Nitrogen and Carbon-Sulfur Bond Formation

Abstract

Carbon-heteroatom bonds are enormously found in both natural and synthetic products which play vital role in polymer chemistry, material science, agriculture and pharmaceutical industry. Due to prevalence of these bonds, development of new and efficient methods for their construction is of great significance. Transition metal catalysis has revolutionized the way these bonds are formed. Number of methodologies has been developed to form C-heteroatom bonds employing transition metals as catalysts. Transition metal mediated cross-coupling reactions to form C-N, C-O and C-S bonds have been greatly improved by using ligands. Mono-amides of dipicolinic acid are discovered to efficiently act as ligands for copper catalyzed C-N and C-S cross coupling reactions. These ligands are highly stable. Mono-amide of ethylamine was found to be the most efficient ligand after the careful screening of all the available mono-amides of dipicolinic acid. Best working conditions for mono-amide of ethylamine were found after successful screening of each reaction parameter such as solvent, base, temperature and molar ratio of base. The scope of newly discovered catalytic system was investigated by the arylation of various amides and aromatic thiols using differently substituted iodobenzenes. All the coupled products were obtained in good to excellent yields. Synthesized products were characterized by physical and spectroscopic techniques.