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Item Direct catalytic synthesis of β-(C3)-substituted pyrroles: a complementary addition to the Paal–Knorr reaction(RSC, 2021) Kumar, IndreshThe synthesis of β-(C3)-functionalized pyrroles is a challenging task and requires a multistep protocol. An operationally simple direct catalytic synthesis of β-substituted pyrroles has been developed. This one-pot multicomponent method combined aqueous succinaldehyde as 1,4-dicarbonyl, primary amines, and isatins to access hydroxyl-oxindole β-tethered pyrroles. Direct synthesis of the β-substituted free NH-pyrrole is the central intensity of this work. DFT-calculations and preliminary mechanism investigation support the possible reaction pathway.Item Two-pot synthesis and photophysical studies of 1,6-disubstituted 5-aza-indoles from succinaldehyde and N-aryl propargylic-imines(RSC, 2021) Kumar, IndreshA two-pot synthesis of 5-aza-indoles has been developed from aqueous succinaldehyde and N-aryl propargylic-imines. This overall protocol involves: (i) the metal-free [3 + 2] annulation of aqueous succinaldehyde and N-aryl propargylic-imines to access 2-alkynyl-pyrrole-3-aldehydes and (ii) Ag-catalyzed 6-endo-dig-cyclization to obtain substituted 5-aza-indoles in the second pot. The 5-aza-indoles showed engaging photophysical activities, and the practicality of this pot-economic gram-scale synthesis has been demonstrated.Item Synthesis of hybrid 1,2,3-triazolo-δ-lactams/lactones using Huisgen [3+2] cycloaddition ‘click-chemistry’ in water(Elsiever, 2010-03) Kumar, IndreshThe synthesis of a new class of hybrid 1,2,3-triazozlo-δ-lactams/lactones has been achieved using the Huisgen [3+2] dipolar cycloaddition ‘click-chemistry’ reaction of various organic azides with an activated alkyne in water, followed by cyclization.Item Proline catalyzed direct diastereoselective 6-enolexo aldolization: toward the synthesis of the imino sugar DNJ(Elsiever, 2010-11) Kumar, IndreshA l-proline catalyzed direct diastereoselective 6-enolexo aldolization reaction of differentiating dialdehydes derived from tartaric acid is presented. This organocatalytic approach provides high levels of syn-selectivity (dr >10:1) with the stereocontrolled C–C bond formation between C4 and C5 intramolecularly, which can serve to synthesize imino-sugar skeleton quickly.Item Intramolecular Huisgen [3+2] cycloaddition in water: synthesis of fused pyrrolidine–triazoles(Elsiever, 2012-02) Kumar, IndreshThe intramolecular alkyne–azide Huisgen [3+2] cycloaddition reaction as a ‘click-chemistry’ reaction without a metal catalyst has been studied under aerobic conditions. The synthesis of various pyrrolidine–triazole hybrid compounds has also been achieved by using this intramolecular cycloaddition reaction in water with complete 1,5-regioselectivity.Item 1,3-Carbon D–A strategy for [3 + 2] cycloadditions/annulations with imines: synthesis of functionalized pyrrolidines and related alkaloids(RSC, 2014) Kumar, IndreshCycloaddition/annulation reactions remain the most attractive methods for the synthesis of five membered heterocyclic ring systems. Among the three possible strategies for [3 + 2] cycloaddition, this review focuses on 1,3-carbon donor–acceptor (C3, D–A) cycloaddition/annulation reactions with imines to synthesize pyrrolidines. The formal [3 + 2] cycloaddition, which includes the in situ 1,3-carbon D–A precursor generation through metal catalysis, Lewis acid catalysis and organocatalysis approaches is highlighted. The scope and limitations of this strategy along with its applications in the synthesis of natural product alkaloids reported during the last decade are outlined.Item Direct catalytic synthesis of densely substituted 3-formylpyrroles from imines and 1,4-ketoaldehydes(RSC, 2014) Kumar, IndreshA sustainable method for the direct access to highly substituted 3-formylpyrroles from 1,4-ketoaldehydes and imine via formal [3 + 2] cycloaddition is reported. This reaction involves a one-pot amine catalyzed chemoselective Mannich-cyclization-aerobic oxidation sequence with good to high yields. Further application of the gram scale reaction as well as synthesis of fully substituted 3-formylpyrrole is also shown.Item Enantioselective synthesis of 1,2,5,6-tetrahydropyridines (THPs) via proline-catalyzed direct Mannich-cyclization/domino oxidation–reduction sequence: application for medicinally important N-heterocycles(RSC, 2016) Kumar, IndreshAn enantioselective multi-component synthesis of 1,2,5,6-tetrahydropyridines (THPs) has been developed through a one-pot domino-process. This transformation proceeds through proline-catalyzed direct Mannich reaction-cyclization of glutaraldehyde with in situ generated imines, followed by site-selective oxidation–reduction sequence under mild conditions. Chiral 1,2,5,6-THPs are obtained in good to high yields (up to 80%) and with the excellent enantioselectivity (up to 98 : 2 er). The usefulness of this operationally simple method is also shown to synthesize other medicinally important nitrogen-heterocycles.Item Synthesis of Quinazolinones, Imidazo[1,2-c]quinazolines and Imidazo[4,5-c]quinolines through Tandem Reductive Amination of Aryl Halides and Oxidative Amination of C(sp3)–H Bonds(Wiley, 2016-11-03) Kumar, IndreshThe synthesis of quinazolinones, imidazo[1,2-c]quinazolines and imidazo[4,5-c]quinolones has been achieved through a multicomponent copper-catalyzed reaction using easily available sodium azide as a nitrogen source, and DMA (N,N-dimethylacetamide) as a one-carbon source. N-Fused heterocycles were obtained in good to excellent yields, and the reaction is suitable for gram-scale synthesis.Item An Unprecedented Pseudo-[3+2] Annulation between N-(4-Methoxyphenyl)aldimines and Aqueous Glutaraldehyde: Direct Synthesis of Pyrrole-2,4-dialdehydes(Wiley, 2017-04-26) Kumar, IndreshThe 2-iodoxybenzoic acid (IBX)-mediated oxidative rearrangement of tetrahydropyridine intermediates, prepared through proline-catalyzed annulation between glutaraldehyde and imines, is explored as a means for the regioselective synthesis of pyrrole-2,4-dialdehydes. PMP = 4-MeOC6H4.