Graphene oxide: an efficient carbocatalyst for the solvent-free synthesis of 2-(substituted benzoyl)-3-(substituted phen
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Graphene oxide: an efficient carbocatalyst for the solvent-free synthesis of 2-(substituted benzoyl)-3-(substituted phenyl)imidazo[1,2-a]pyridines DILPREET KOURa,b, SONAKSHI SASANa and KAMAL K KAPOORa,* a Department
of Chemistry, University of Jammu, Jammu 180 006, India of Chemistry, University Institute of Engineering and Technology, Kathua, University of Jammu, Jammu 184 103, India E-mail: [email protected] b Department
MS received 28 May 2019; revised 13 August 2019; accepted 15 August 2019
Abstract. GO has been found as a remarkable heterogeneous carbocatalyst for the solvent-free synthesis of 2-(substituted benzoyl)-3-(substituted phenyl)imidazo[1,2-a]pyridines from chalcones and 2-aminopyridine. The present methodology offers a novel and eco-friendly approach with appreciable yields of the desired products. Keywords. 2-(Substituted benzoyl)-3-(substituted phenyl)imidazo[1,2-a]pyridines; GO; carbocatalyst; solvent free; recyclability.
1. Introduction Imidazo[1,2-a]pyridines possess a variety of biological activities1 such as antiulcer,2 antibacterial,3 antipyretic,4 antiviral,5 anti-inflammatory,6 andanticancer.7 This nucleus has gained importance due to its contribution in the area of material science, optoelectronics8 and organometallics.9 The therapeutic potential of this nucleus makes it serve as an integral core of various commercially available drugs as shown in (Figure 1).10 The diversification of applications of this framework generates immense interest among organic chemists to devise newer better protocols for its synthesis. Since this nucleus is associated with a wide range of biological activities,1 various analogues of imidazopyridine have been synthesized.11 One of them is (substituted benzoyl)imidazo[1,2-a]pyridine in which substituted benzoyl functionality has been held accountable for its eminent biological properties.12 With the advances in green and sustainable chemistry, the development of solvent-free methodologies using heterogeneous catalysts has
been gaining prime interest.13 In this regard, Graphene oxide (GO) has evolved as an efficient organic material appreciated as being eco-friendly and versatile carbocatalyst14 due to its remarkable features like stability, biocompatibility, large surface area and promising electronic, optical, thermal and mechanical properties.15 The surface of graphene oxide is functionalized with several oxygencontaining groups like carboxyl, epoxy and hydroxyl groups. These functionalities are responsible for the oxidising properities16 and the acidic nature (pH 4.5 at 0.1 mg mL-1)17 of GO (Figure 2). Owing to their excellent merits of low toxicity and recyclability, Go has played a significant role in carrying out wide range of synthetic organic transformations.18 Recently, an iodine mediated preparation of imidazo[1,2-a]pyridines19 has been established in our laboratory. In our quest towards the development of an ecobenign protocol for the preparati
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