Synthesis of Imidazo 1 2 a pyridines and their Functionalization via C C and C N Bond Formation using Transition Metal Catalysts

Abstract

Imidazo[1,2-a]pyridine is an important heterocylic motif which is widely present in a range of biological active compounds as well as in compounds with interesting optoelectronic properties. Synthesis and newlinefunctionalization of imidazo[1,2-a]pyridine with novel methods is desired both from economic and environmental point of view. The current thesis focuses on synthesis of imidazo[1,2-a]pyridines and their functionalization via C C and C N bond formation using transition metal catalysts. In this thesis, synthesis of 3-aroylimidazo[1,2-a]pyridine has been achieved using inexpensive copper catalyst and further functionalization of imidazo[1,2-a]pyridine has been achieved using copper and vanadium catalyst. A brief outline of the work presented in the thesis is given below. newlineThe first chapter of the thesis describes the synthesis of 3-aroylimidazo[1,2-a]pyridines using copper catalyst. This chapter is divided into two parts. Part A described the reaction of different substituted newlinechalcones and a range of 2-aminopyridines. The reaction conditions are benign, require shorter reaction time and furnished good yields of 3-aroylimidazo[1,2-a]pyridine with a variety of substrates. All synthesized product were characterized using NMR, IR and mass spectroscopic technique. In part B, we newlinehave further improved the methodology for the synthesis of 3-aroylimidazo[1,2-a]pyridines through onepot, three-component tandem reaction. Use of simple and readily available precursors like acetophenones, aldehydes and 2-aminopyridines, synthesis of functionalized bio-active imidazo[1,2-a]pyridines, single step reaction, atom and step-economy, simple isolation procedures, moderate to good newlineyields of tandem products, air as a sole oxidant, and good functional group tolerance are the salient features of the method. newlineThe second chapter of the thesis describes a simple and highly efficient protocol for the regioselective synthesis of azole-substituted imidazo[1,2-a]pyridines using ligand-free, copper-catalyzed Ullmann-type C N coupling reaction.