BITS Faculty Publications
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Item Mechanochemical Ruthenium-Catalyzed Ortho-Alkenylation of N-Heteroaryl Arenes with Alkynes under Ball-Milling Conditions(ACS, 2022-04) Kumar, AnilThe mechanochemical, solvent-free Ru(II)-catalyzed alkenylation of N-heteroaryl arenes with alkynes has been successfully described. A wide spectrum of arenes bearing N-heteroaryl moieties such as imidazo[1,2-a]pyridine, imidazo[1,2-a]pyrimidine, benzo[d]imidazo[2,1-b]thiazole, imidazo[2,1-b]thiazole, 2H-indazole, 1H-indazole, 1H-pyrazole, and 1,2,4-oxadiazol-5(4H)-one as a directing group reacted with various substituted alkynes under ball milling in the presence of [Ru(p-cymene)Cl2]2, affording dialkenylated products in moderate to good yields. The reaction of 2,3-dihydrophthalazine-1,4-dione with 1-phenyl-1-propyne afforded a monoalkenylated product. Similarly, reaction of 2-phenylimidazo[1,2-a]pyridine with aliphatic terminal alkynes produced a monoalkenylated derivative as the major product along with minor amount of dialkenylated product. The developed method exhibited excellent functional group compatibility, broad substrate scope, shorter reaction times, and no external heating. Moreover, the method can be readily scaled-up as demonstrated by gram-scale synthesis of 2-(2,6-bis((E)1-phenylprop-1-en-2-yl)phenyl)imidazo[1,2-a]pyridine.Item Design and Synthesis of a Palladium(II) Complex of a CNHCNN Pincer-Type N-Heterocyclic Carbene Ligand: Application towards the Oxidative Amidation of Aldehydes with 2-Aminopyridines(ACS, 2023-08) Kumar, AnilThis report describes the synthesis of a [CNHCNN]-pincer-type palladium(II) complex bearing a N-heterocyclic carbene (NHC)-derived pincer CNN ligand. The ligand and palladium pincer complex were characterized with the help of 1H, 13C{1H} NMR, Fourier transform infrared (FTIR) spectroscopy, high-resolution mass spectrometry (HRMS), ultraviolet–visible (UV–vis) spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The coordination mode of the ligand with the palladium was confirmed using single-crystal X-ray diffraction studies. The complex possesses a distorted square planar geometry around the palladium center. The Pd(II) pincer complex was used as a catalyst for the oxidative amidation of aldehydes with 2-aminopyridines. Notably, only 1.0 mol % catalyst loading is required to activate a wide range of substrates under mild reaction conditions. The protocol showed excellent tolerance toward a diverse range of functional groups with good to very good yields (up to 88%) of amidation products. A plausible mechanism of the amidation reaction is proposed on the basis of control experiments.Item Catalyst-Controlled Regiodivergent Oxidative Annulation of 2-Arylimidazo[1,2-a]pyridines with Cinnamaldehyde Derivatives for Construction of Fused N-Heterocyclic Framework(ACS, 2023-09) Kumar, AnilCatalyst-dependent regioselective oxidative annulation of 2-arylimidazo[1,2-a]pyridines with cinnamaldehyde derivatives to construct fused N-heterocyclic frameworks has been described. The annulation reaction afforded 5-arylnaphtho[1′,2′:4,5]imidazo[1,2-a]pyridine-6-carbaldehydes in the presence of [RhCp*Cl2]2 as catalyst while 1,7-diarylimidazo[5,1,2-cd]indolizine-6-carbaldehydes were obtained using Pd(OAc)2 as catalyst. The reaction produced annulated products in good yields and exhibited broad substrate scope and excellent functional group tolerance. The method provides two different isomeric annulated products bearing an aldehyde functionality which can be elaborated into an array of functionalities leading to valuable compounds.Item A Simple and Efficient Synthesis of 2,3-Diarylnaphthofurans Using Sequential Hydroarylation/Heck Oxyarylation(ACS, 2013) Kumar, AnilAn efficient and simple strategy has been developed for the synthesis of 2,3-diarylnaphthofurans using sequential hydroarylation of naphthols and alkynes in the presence of In(OTf)3 under microwave irradiation followed by one-pot Heck-oxyarylation of generated 1-substituted-α-hydroxy styrenes.Item Povarov-Reductive Amination Cascade to Access 6-Aminoquinolines and Anthrazolines(ACS, 2013) Kumar, AnilA new strategy is reported for the synthesis of 6-aminoquinoline derivatives via a tandem Povarov reaction, dihydroquinoline oxidation, and imine reduction. These products allow access to symmetrical as well as unsymmetrical tetraarylpyrido[2,3-g]quinolines, potentially useful organic electronicsItem Copper-Catalyzed Tandem Azide–Alkyne Cycloaddition, Ullmann Type C–N Coupling, and Intramolecular Direct Arylation(ACS, 2013) Kumar, Anil; Khungar, BhartiA ligand-free copper-catalyzed tandem azide–alkyne cycloaddition (CuAAC), Ullmann-type C–N coupling, and intramolecular direct arylation has been described. The designed strategy resulted in the synthesis of a novel trazole-fused azaheterocycle framework. The reaction gave good yields (59–77%) of 1,2,3-triazole-fused imidazo[1,2-a]pyridines in a single step.Item NEXT Oxidative Cross-Coupling of sp3- and sp2-Hybridized C–H Bonds: Vanadium-Catalyzed Aminomethylation of Imidazo[1,2-a]pyridines(ACS, 2015-10-19) Kumar, AnilThe vanadium-catalyzed oxidative coupling of substituted 2-arylimidiazo[1,2-a]pyridines to N-methylmorpholine oxide, which acts as both a coupling partner and an oxidant, has been achieved. This reaction was applied to various substituted imidiazo[1,2-a]pyridine and indole substrates, resulting in yields as high as 90%. Mechanistic investigations indicate that the reaction may proceed via a Mannich-type process. This work demonstrates how oxidative aminomethylation can be used as a useful method to introduce tertiary amines into heterocycles, thus providing an alternative method for conventional Mannich-type reactions.Item Ruthenium(II)-Catalyzed Regioselective Ortho Amidation of Imidazo Heterocycles with Isocyanates(ACS, 2016) Kumar, Anil; Sakhuja, RajeevDirect ortho amidation at the phenyl ring of 2-phenylimidazo heterocycles with aryl isocyanates has been achieved via a chelation-assisted cationic ruthenium(II) complex catalyzed mechanism. The methodology provides a straightforward, high-yielding regioselective approach toward the synthesis of an array of ortho-amidated phenylimidazo heterocycles without prior activation of C(sp2)–H. This also reports the first method for coupling of aryl isocyanates with the imidazo[1,2-a]pyridine system via a pentacyclometalated intermediate. The methodology is found to be easily scalable and could be applied toward the selective ortho amidation of 2-heteroarylimidazo[1,2-a]pyridine frameworks.Item Design and Syntheses of Palladium Complexes of NNN/CNN Pincer Ligands: Catalyst for Cross Dehydrogenative Coupling Reaction of Heteroarenes(ACS, 2020) Kumar, AnilThis report describes simple syntheses of a new class of palladium(II) pincer complexes having NNN and CNN coordination modes. The new complexes were fully characterized with the help of 1H and 13C{1H} NMR, HRMS, and IR spectroscopy. The structure and bonding modes of complexes were further authenticated with the help of single-crystal X-ray diffraction. Thermally robust and moisture-/air-insensitive palladium pincer complexes C1–C4 have been used as catalysts for cross dehydrogenative coupling (CDC) reactions of two heteroarenes and found to be very efficient. The catalyst was successful in activating the C–H bond of a variety of heteroarenes, including benzimidazole, imidazole, benzothiazole, imidazopyridine, thiophene, and furan, with only 1.0 mol % of catalyst, achieving excellent yields of the coupled products. The catalyst showed excellent tolerance toward functional groups such as CHO, COMe, COOMe, COOEt, CONHPh, Me, CN, Br, and Cl. Further, the catalyst is reusable up to four reaction cycles with only a minor loss in its efficiency. The mechanism of the CDC reaction was investigated through control experiments, and it has been suggested that a palladium acetate analogue of the NNN pincer ligand (C5) is the active catalyst.Item Rhodium(III)-Catalyzed Dehydrogenative Annulation and Spirocyclization of 2-Arylindoles and 2-(1H-Pyrazol-1-yl)-1H-indoles with Maleimides: A Facile Access to Isogranulatimide Alkaloid Analogues(ACS, 2021) Kumar, Anil; Kumar, DalipA Rh(III)-catalyzed dehydrogenative annulation and spirocyclization of 2-arylindoles and 2-(1H-pyrazol-1-yl)-1H-indole with maleimides is described. The cascade protocol provided highly functionalized benzo[a]pyrrolo[3,4-c]carbazole-1,3(2H,8H)-diones and spiro[isoindolo[2,1-a]indole-6,3′-pyrrolidine]-2′,5′-diones in good to excellent. The developed reaction methodology exhibited broad substrate scope with good functional group tolerance and is operationally simple and scalable. Photophysical properties of the annulated products were investigated. The annulated product of 2-(1H-pyrazol-1-yl)-1H-indole showed high absorption and emission values with a large red-shift as compared to that of 2-phenylindole.