PIDA as an Iodinating Reagent: Visible-Light-Induced Iodination of Pyrazolo[1,5-a]pyrimidines and Other Heteroarenes.

We have developed a visible-light-mediated convenient and efficient strategy for the iodination of heteroarenes using diacetoxyiodobenzene (PIDA) under photocatalyst-free conditions. This unique approach is the first report on photocatalytic C-H iodination employing PIDA as the iodinating agent. The new photocatalyst-free strategy is applicable to a wide range of pyrazolo[1,5-a]pyrimidine derivatives with various functionalities.

Tunable Regioselective Allylic Alkylation/Iodination of Imidazoheterocycles in Water.

The switchable roles of allylic alcohol and molecular iodine as reagents and catalysts have been demonstrated in the regioselective allylic alkylation and iodination of imidazoheterocycles employing the mixture of allylic alcohol-I. First, we have explored the catalytic activity of iodine for the allylation of imidazoheterocycles using allylic alcohol in an aqueous medium. The allylation of a library of imidazoheterocycles and other electron-rich heterocycles like indole, pyrazole, 4-hydroxy coumarin, and 6-amino uracil has been achieved by employing this methodology.

KSO-Promoted Consecutive Tandem Cyclization/Oxidative Halogenation: Access to 3-Halo-Pyrazolo[1,5-]pyrimidines.

A one-pot methodology has been developed to synthesize 3-halo-pyrazolo[1,5-]pyrimidine derivatives through the three-component reaction of amino pyrazoles, enaminones (or chalcone), and sodium halides. The use of easily accessible 1,3-biselectrophilic reagents like enaminones and chalcone offers a straightforward approach for the synthesis of 3-halo-pyrazolo[1,5-]pyrimidines. The reaction proceeded through a cyclocondensation reaction between amino pyrazoles with enaminones/chalcone in the presence of KSO followed by oxidative halogenations by NaX-KSO.

Visible-Light-Mediated Regioselective C3-H Selenylation of Pyrazolo[1,5-]pyrimidines Using Erythrosine B as Photocatalyst.

A visible-light-induced efficient methodology has been developed for the C-H selenylation of pyrazolo[1,5-]pyrimidine derivatives employing erythrosine B as the photocatalyst. This is the first report on the regioselective selenylation of pyrazolo[1,5-]pyrimidines. The efficiency of this methodology for the selenylation of different electron-rich heterocycles like pyrazole, indole, imidazo[1,2-]pyridine, imidazo[2,1-]thiazole, and 4-(phenylamino)-2-chromen-2-one has been also demonstrated.

Visible-Light-Induced Regioselective C-H Sulfenylation of Pyrazolo[1,5-]pyrimidines via Cross-Dehydrogenative Coupling.

A visible-light-induced cross-dehydrogenative methodology has been developed for the regioselective sulfenylation of pyrazolo[1,5-]pyrimidine derivatives. Rose bengal, blue LEDs, KI, KSO, and DMSO are all essential for this photocatalytic transformation. The protocol is applicable for the synthesis of a library of 3-(aryl/heteroaryl thio)pyrazolo[1,5-]pyrimidine derivatives with broad functionalities.

Visible light-promoted photocatalyst-free activation of persulfates: a promising strategy for C-H functionalization reactions.

The employment of renewable energy resources is highly desirable according to the twelve principles of green chemistry. In this context, visible light promoted organic transformations have gained much attention from synthetic chemists due to the employment of renewable energy. However, the inability of the majority of organic molecules to absorb visible light encouraged the use of photocatalysts in visible light-mediated organic transformations.

Recent advances in the synthesis of fluorinated compounds via an aryne intermediate.

The development of new methodologies for the synthesis of fluorinated organic molecules is in high demand due to their wide applications in agriculture and pharmaceutical sciences. Various strategies have been employed for this purpose for a long time. Arynes are well known synthetic intermediates and have gained the attention of synthetic chemists for the synthesis of various functionalized organic molecules.

Visible light promoted C-H functionalization of imidazoheterocycles.

Direct C-H functionalization is very important in the late-stage functionalization of drug molecules. In this context, visible light promoted transformations have emerged as a green strategy for C-H functionalization compared to the conventional strategy. Various methodologies have been developed for the C-H functionalization of different bioactive heterocycles employing this visible light photocatalysis in the presence of either transition metal photocatalysts or organophotoredox catalysts and even in the absence of any photocatalyst.

Visible-Light-Promoted C(sp)-C(sp) Cross-Dehydrogenative Coupling of Tertiary Amine with Imidazopyridine.

A metal-free visible-light-promoted C(sp)-C(sp) cross-dehydrogenative coupling between tetrahydroisoquinoline and imidazo[1,2- a]pyridine has been developed to afford 3-substituted imidazopyridines using a catalytic amount of rose bengal as photosensitizer under aerobic conditions. The present methodology is also applicable to imidazo[1,2- a]pyrimidine, indolizine, indole, and pyrrole as well as N, N-dimethyl aniline. Wide substrates scope, use of organo photocatalyst, metal-free, and mild reaction conditions are the attractive features of this methodology.

C-Glycosidation of Unprotected Di- and Trisaccharide Aldopyranoses with Ketones Using Pyrrolidine-Boric Acid Catalysis.

C-Glycoside derivatives are found in pharmaceuticals, glycoconjugates, probes, and other functional molecules. Thus, C-glycosidation of unprotected carbohydrates is of interest. Here the development of C-glycosidation reactions of unprotected di- and trisaccharide aldopyranoses with various ketones is reported.

Design, Synthesis, and Functionalization of Imidazoheterocycles.

Over the years, various strategies have been reported for the synthesis of imidazo[1,2-a]pyridines due to their importance in different fields. In this account, we represent the methods developed by our group for the synthesis and functionalization of imidazo[1,2-a]pyridines. Different synthetic strategies have been developed using easily accessible reactants for this purpose.

Iodine-catalyzed regioselective thiolation of imidazo[1,2-a]pyridines using sulfonyl hydrazides as a thiol surrogate.

Iodine-catalyzed regioselective sulfenylation of imidazo[1,2-a]pyridines via C(sp(2))-H bond functionalization has been achieved using sulfonyl hydrazides as a thiol surrogate. A library of 3-sulfanylimidazopyridines with broad functionalities was synthesized under metal and oxidant-free practical reaction conditions. This methodology is also applicable for the regioselective sulfenylation of imidazo[2,1-b]thiazole and benzo[d]imidazo[2,1-b]thiazole.

Regioselective oxidative trifluoromethylation of imidazoheterocycles via C(sp2)-H bond functionalization.

Catalytic oxidative trifluoromethylation of imidazopyridines has been carried out at room temperature through the functionalization of the sp(2) C-H bond employing Langlois reagent under ambient air. A library of 3-(trifluoromethyl)imidazo[1,2-a]pyridines with broad functionalities have been synthesized regioselectively. This methodology is also applicable to imidazo[2,1-b]thiazole and benzo[d]imidazo[2,1-b]thiazole.

Synthesis of imidazo[1,2-a]pyridines: a decade update.

Imidazopyridine is one of the important fused bicyclic 5-6 heterocycles and it is recognized as a "drug prejudice" scaffold due to its wide range of applications in medicinal chemistry. This moiety is also useful in material science because of its structural character. Synthesis of this moiety from the easily available chemicals is desirable due to its tremendous use in the various branches of chemistry.

Unprecedented catalytic activity of Fe(NO3)3·9H2O: regioselective synthesis of 2-nitroimidazopyridines via oxidative amination.

A unique iron-catalyzed oxidative diamination of nitroalkene with 2-aminopyridine for the synthesis of 2-nitro-3-arylimidazo[1,2-a]pyridines with complete regioselectivity has been achieved under mild and aerobic reaction conditions. This is the first method for the synthesis of 2-nitroimidazo[1,2-a]pyridines. These scaffolds were also synthesized directly from styrenes.

Functionalization of an sp(3) C-H bond via a redox-neutral domino reaction: diastereoselective synthesis of hexahydropyrrolo[2,1-b]oxazoles.

A diastereoselective synthesis of pyrrolidinooxazolidines was achieved by a metal-free, base-promoted reaction of pyrrolidine and aromatic aldehydes under microwave irradiation. The rare functionalization of an sp(3) C-H bond probably results from an in situ generated azomethine ylide that undergoes cycloaddition with aldehydes.