Department of Chemistry
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Item Tandem transformation of indazolones to quinazolinones through pd-catalyzed carbene insertion into an n–n bond(ACS, 2023-01) Shakuja, RajeevSerendipitous and expedite transformation of 1-aryl- and 2-aryl-1,2-dihydro-3H-indazol-3-ones to 1,2-di(hetero)aryl- and 2,3-di(hetero)aryl-2,3-dihydroquinazolin-4(1H)-ones, respectively, was achieved in high efficiency by reacting them with aldehydic N-tosylhydrazones. The protocol proceeded through a cascade process involving base-mediated Pd-carbenoid generation by the decomposition of N-tosylhydrazones, nucleophilic attack of indazolone on the Pd-carbenoid complex, and intramolecular ring expansion via N–N bond cleavage. The utility of the strategy is demonstrated toward the synthesis of bioactive NPS 53574, a calcium receptor antagonist.Item RH(III)-catalyzed fabrication of [4,3,1]-bridged azaheterocycles using quinone monoacetals(ACS, 2025-06) Sakhuja, RajeevA rhodium-catalyzed annulation strategy for the fabrication of cyclohexanone-bridged indazolones and other related diazole-ones and diazine-ones was established using quionone monoacetals under mild conditions. On the other hand, the use of 4-hydroxy-4-methylcyclohexa-2,5-dienone under the optimized Rh-conditions produced an ortho-CAr-arylated product in moderate reactivity. Mechanistic studies suggested that the coupling proceeded via one-pot C–H activation-Michael/hetero-Michael additions into the enone moiety. Interestingly, the [4,3,1]-bridged-1,2-dihydro-3H-indazol-3-ones underwent unexpected migratory aromatization in acidic condition to produce 3-hydroxy-14H-benzo[c]indazolo[1,2-a]cinnolin-14-ones in high yields.Item Electrochemical Oxidative Coupling Between Benzylic C(sp3)–H and N–H of Secondary Amines: Rapid Synthesis of α-Amino α-Aryl Esters(ACS, 2021-06) Kumar, IndreshAn intermolecular electrochemical coupling between the benzylic C(sp3)–H bond and various secondary amines is reported. The electronic behavior of two electronically rich units viz the α-position of α-aryl acetates and amines was engineered electrochemically, thus facilitating their reactivity for the direct access of α-amino esters. A series of acyclic/cyclic secondary amines and α-aryl acetates were tested to furnish the corresponding α-amino esters with high yields (up to 92%) under mild conditions.Item Asymmetric Synthesis of Bridged N-Heterocycles with Tertiary Carbon Center through Barbas Dienamine-Catalysis: Scope and Applications(ACS, 2021-11) Kumar, Indresh; Kumar, DalipA direct aza-Diels–Alder reaction between 2-aryl-3H-indolin-3-ones and cyclic-enones has been developed to access chiral indolin-3-one fused polycyclic bridged compounds. This method proceeds via proline-catalyzed Barbas-dienamine intermediate formation from various cyclic-enones such as 2-cyclopenten-1-one, 2-cyclohexene-1-one, and 2-cycloheptene-1-one, followed by a reaction with 2-aryl-3H-indol-3-ones. Several indolin-3-ones fusing [2.2.2], [2.2.1], and [3.2.1] skeletons decorated with a tertiary carbon chiral center have been prepared. Computational studies (DFT) supported the observed stereoselectivity in the method. The synthesized compounds have shown exciting photophysical activities and selective sensing of Pd2+ and Fe3+ ions through the fluorescence quenching “switch-off” mode.Item Phenyliodine(III) Diacetate-Mediated 1,2-ipso-Migration in Mannich Bases of Imidazo[1,2-a]pyridines: Preparation of N-Acetoxymethyl/Alkoxymethyl-N-arylimidazo[1,2-a]pyridine-3-amines(ACS, 2020-05) Kumar, AnilPhenyliodine(III) diacetate -mediated 1,2-ipso-migration of an imidazo[1,2-a]pyridine ring via the formation of an aziridine intermediate in Mannich bases derived from imidazo[1,2-a]pyridines, 2-pyridylamines or arylamines, and formaldehyde is reported. The imidazo[1,2-a]pyridines bearing different substituents showed excellent migratory aptitude and resulted in corresponding N-acetoxymethyl-, N-alkoxymethyl-, and N-hydroxymethyl-N-arylimidazo[1,2-a]pyridine-3-amine derivatives in moderate to excellent (42 examples; 35–93%) yields. Radical trapping experiments confirmed the involvement of a non-radical intermediate. The developed protocol is amenable for a scale-up reaction, and synthetic utility of N-acetoxymethyl products was demonstrated by transforming them to corresponding N-(pyridin-2-yl)imidazo[1,2-a]pyridin-3-aminesItem KPF6-Mediated Esterification and Amidation of Carboxylic Acids(ACS, 2022-01) Kumar, AnilA novel KPF6-promoted green method has been developed for the synthesis of esters and amides. A wide range of carboxylic acids and alcohols or amines worked well under the developed reaction conditions, thus providing good to excellent (61–98%) yields of the corresponding esters and amides. The method worked well with bioactive substrates such as cholesterol, levulinic acid, and linoleic acid. Wide substrate scope, operational simplicity, scalability, and sustainability make this protocol a practical and economically attractive approach for the preparation of ester and amides.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 White Light Emission in Butadiyne Bridged Pyrene–Phenyl Hybrid Fluorophore: Understanding the Photophysical Importance of Diyne Spacer and Utilizing the Excited-State Photophysics for Vapor Detection(ACS, 2016-07) Pati, Avik K.Generation of white light emission (WLE) from a single organic fluorophore is challenging because of the need to get fluorescence covering the visible region (400–700 nm) upon excitation of the dye at near-ultraviolet wavelength. Herein, we report WLE from a butadiyne bridged pyrene–phenyl hybrid fluorophore in mixed-aqueous solvents as well as in polymer film matrices. The ability of the butadiynyl dye to emit from multiple excited states such as locally excited (LE; 400–500 nm), aggregate (excimer type; 475–600 nm), and charge transfer (CT; 500–750 nm) states spanning the emission almost throughout the visible range has made the generation of the white light to be possible. In highly polar solvent such as acetonitrile, the butadiynyl dye emits from the LE and CT states, and the WLE is achieved through a control of the dye concentration such that intermolecular CT (exciplex type) contributes along with the intramolecular CT and LE emissions. In mixed-aqueous systems such as water–acetonitrile and water–N,N-dimethylformamide, the CT emission is red-shifted (because of the high dielctric constant of water), and the contribution of the aggregate emission (originated because of the poor solvent water) is important in maintaining the relative distribution of the fluorescence intensities (LE, excimer, and CT) in the entire visible region. The significance of the diyne spacer in achieving the WLE is delineated through a control study with a single acetylenic analogue. The LE, aggregate, and CT emissions are involved in generating bluish-white light in a poly(vinyl alcohol) film matrix of the butadiynyl dye. Blue emission is noted in a poly(methyl methacrylate) (PMMA) film matrix of the dye with a major contribution from the LE and a minor contribution from the aggregate state. Exposure of the PMMA film of the dye to polar aprotic vapors assists in gaining the CT state emission such that the LE, aggregate, CT emissions cover the entire visible region to produce the WLE. This opens a new strategy for selective vapor sensing.Item Reducing-Agent-Free Convergent Synthesis of Hydroxyimino-Decorated Tetracyclic Fused Cinnolines via RhIII-Catalyzed Annulation Using Nitroolefins(ACS, 2021-01) Sakhuja, RajeevA mild Rh-catalyzed method was developed for the synthesis of hydroxyimino functionalized indazolo[1,2-a]cinnolines and phthalazino[2,3-a]cinnolines by reductive [4 + 2] annulation between 1-arylindazolones and 2-aryl-2,3-dihydrophthalazine-1,4-diones with varied nitroolefins. The targeted oxime decorated tetracyclic fused cinnolines were synthesized via sequential C–H activation/olefin insertion/reduction under reducing-agent-free conditions.Item Palladium-Catalyzed Weakly Coordinating Lactone-Directed C–H Bond Functionalization of 3-Arylcoumarins: Synthesis of Bioactive Coumestan Derivatives(ACS, 2021) Kumar, Anil; Kumar, DalipA palladium-catalyzed highly regioselective ortho-selective C–H functionalization of 3-arylcoumarins has been developed. The method utilizes the weakly coordinating lactone as a directing group. The versatility of the strategy is highlighted by developing methodologies for alkenylation, halogenation, fluoroalkoxylation, and hydroxylation. Different functional groups were well tolerated, and functionalized coumarins were obtained in moderate to high yields. The method also showed good selectivity for monofunctionalization versus difunctionalization. The generated ortho-hydroxy derivatives were cyclized in the presence of DDQ, thus developing a simple and fast method for the synthesis of bioactive coumestan from 3-arylcoumarins.