Chan-Evans-Lam coupling for the synthesis of N-aryl derivatives catalyzed by copper(I) chloride and sterically varied imidazolium salts at mild reaction conditions

First-row transition-metal-catalyzed organic transformations have received colossal interest in the modern synthetic organic chemistry due to their step- and atom-economic approaches. As a consequence, direct arylation of azoles through C-H or N-H activations acquired a broad spectrum of applications for accessing valuable small organic molecules that are of pharmaceutical interest. In this connection, sterically varied coumarin-functionalized imidazolium salts bearing bromide (5-7) and hexafluorophosphate anions (8-10) have been prepared and used as NHC precursors. The salts have been characterized by both, spectroscopic and analytical techniques. A hexafluorophosphate salt 9 was also studied for its structure using the single-crystal XRD technique. The salts that indeed, generate carbene that trap Cu(I) to form Cu(I)-NHC complexes in situ for the Chan-Evans-Lam C-N coupling of 1H-azoles/anilines and phenyl/thiopheneboronic acids, resulting in the formation of N-aryl derivatives in moderate to excellent yields. The structure-activity relationship studies revealed that the steric bulk around the metal center would help increase the catalytic Chan-Evans-Lam C-N coupling potential of the catalysts.