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A simple and highly efficient three-component method using easily available amines, nitrostyrene and diketones in one pot has been developed for synthesis of pyrroles in presence of catalytic amount of iodobenzene and Oxone ® as oxidant. The protocol has been used to afford wide range of pyrroles in moderate to good yields.

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Thiosemicarbazides (I) and bisdiarylthioureas (III), on treatment with a hypervalent iodine reagent, generated in situ from iodobenzene and oxone produce heterocycles (II) and (IV) in good yields.

Moderate to good yields of various 3-nitro-2-arylimidazo[1,2-a]pyridines have been easily achieved in the reaction of 2-aminopyridines and nitrostyrenes in the presence of sodium dichloriodide. The procedure is simple and various functional groups are tolerated in this reaction system.Nitrogen-containing heterocycles are widespread in nature and many synthetic bioactive compounds are based on nitrogen heterocycles; 1 so heterocyclic synthesis continues to provide a focus for the development of novel synthetic methodology. Imidazopyridines are known to be one of the important class of heterocycles in medicinal chemistry and, within this group of heterocycles, imidazo[1,2-a]pyridines derivatives have been widely exploited for as antitubercular, 2 anti-inflammatory, 3 anticancer, 4 anti-HIV, 5 and antimicrobial agents. 6Our group is working on novel methodology using iodine reagents 7 and their applications in the synthesis of bioactive compounds. 8 During our studies, we needed to functionalize 3-nitro-2-arylimidazo[1,2-a]pyridine as a key compound. Very few examples of syntheses of 3-nitro-2-arylimidazo[1,2-a]pyridine have been reported in the literature; these include condensation of 2-aminopyridines with nitrostyrenes; 9a three-component reactions of 2-aminopyridines, aldehydes and nitromethane, 9b and SuzukiMiyaura cross-coupling reactions of 2-chloro-3-nitroimidazo[1,2-a]pyridine. 9c Thus our aim was to develop a simple method for the synthesis of 3-nitro-2-arylimidazo[1,2-a]pyridine.We proposed that this compound could be synthesized using iodine-based reagents. Thus in the initial experiment we carried out the reaction between 2-aminopyridine and nitrostyrene in the presence of aqueous NaICl 2 at room temperature in DMF (Scheme 1), but only a very low yield of the desired 3-nitro-2-phenylimidazo[1,2-a]pyridine was isolated after extended reaction time. However, a higher yield of the desired product was obtained when the reaction mixture was heated at 80 °C and, after optimization of reaction conditions, the best yield was obtained in 1.5 hours, when 0.1 equivalent of aqueous sodium dichloroiodide was used. Reactions were also carried out using different solvents such as DMSO, MeOH, EtOH, and MeCN, but very low yields were observed in each case. Thus DMF was deemed the most suitable solvent for this reaction.