Browsing by Author "Nayak, K.H."

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Base-promoted multicomponent synthesis of 1,2,4-triazole-based hybrids from 1,3-diones, β-nitrostyrenes, and hydrazones
(Royal Society of Chemistry, 2024) Sreelekha, M.K.; Jijin, R.K.; Nayak, K.H.; Babu, B.P.
Herein, we report a metal-free, base-promoted route for the synthesis of hybrid molecular scaffolds in which various 1,3-diones and 1,2,4-triazoles are linked by a benzyl bridge. This three-component, one-pot reaction was accomplished by first treating 4-hydroxycoumarin, trans-β-nitrostyrene, and aldehyde hydrazone in the presence of sodium carbonate. Further, this protocol was successfully expanded to other 1,3-diones, such as dimedone and 4-hydroxy-2-quinolone. A broad substrate scope, mild reaction conditions, and the metal and ligand/additive-free approach are the prominent features of this strategy. © 2024 The Royal Society of Chemistry.
Copper-catalyzed aerobic annulation of hydrazones with dienones: an efficient route to pyrazole-linked hybrid molecules
(Royal Society of Chemistry, 2024) Nayak, K.H.; Jijin, R.K.; Sreelekha, M.K.; Babu, B.P.
A copper-catalyzed aerobic [3 + 2] annulation reaction to access various pyrazole-bound chalcones starting from readily available and cost-effective hydrazones and dienones is reported. These pyrazole-bound chalcones were further utilized effectively to prepare a series of pyrazole-linked hybrid molecules, such as pyrazole-pyrazoline, pyrazole-aziridine, and pyrazole-pyridine hybrids by efficient simple transformations. Synthetically challenging hybrid molecules were obtained in a simple, two-step process with high atom economy under aerobic copper catalysis. © 2024 The Royal Society of Chemistry.
Metal-Free Bisamidation of N-Tosylhydrazones with Carboxylic Acids Promoted by Tetrabutylammonium Iodide and tert-Butyl Hydroperoxide
(American Chemical Society, 2024) Shamnad, A.; Nayak, K.H.; Babu, B.P.
A versatile reaction between N-tosylhydrazones and carboxylic acids to access bisamides is reported. This metal-free, room-temperature reaction was catalyzed by TBAI, while TBHP served as the oxidant. Broad substrate scope and good functional group tolerance are the key features of the strategy. Subsequent intramolecular N-arylation of suitably substituted bisamides readily afforded functionalized 3-indazolones. © 2024 American Chemical Society
Progress in copper-catalysed/mediated intramolecular dehydrogenative coupling
(Royal Society of Chemistry, 2022) Bhaskaran, R.P.; Nayak, K.H.; Sreelekha, M.K.; Babu, B.P.
Transition metal-catalysed C-H functionalization reactions are one of the most efficient synthetic methodologies to construct carbon-carbon and carbon-heteroatom bonds. The initial developments in the field were largely dominated by expensive transition metal catalysts. However, in the past decade, the focus of the catalyst shifted to first-row transition metals and copper catalysis contributed significantly. Abundant, cost-effective, and less toxic copper catalysts are an ideal green alternative to palladium and similar metals. The intramolecular dehydrogenative coupling itself developed as a prominent area of focus as the strategy straightaway affords complex polycyclic scaffolds in one pot. Regioselective activation of inert C-H bonds were made possible with copper catalysts and interestingly, oxygen served as the terminal oxidant in most of the cases. In the present review the focus is on the intramolecular dehydrogenative coupling reactions between carbon-hydrogen and heteroatom-hydrogen bonds to afford carbon-carbon and carbon-hetero atom bonds, catalysed/mediated by copper salts. Though the intermolecular dehydrogenative coupling reactions of copper have already been reviewed more than once, to the best of our knowledge this is the first comprehensive account of copper-based intramolecular dehydrogenative coupling. © 2023 The Royal Society of Chemistry.
Synthesis of 4H-Indazol-4-ones and Fused Pyrazoles via Copper-Catalyzed Annulation of Hydrazones with Cyclic Enones
(John Wiley and Sons Inc, 2023) Nayak, K.H.; Bhaskaran, R.P.; Shamnad, A.; Babu, B.P.
Herein, we report the synthesis of cyclic ketone-fused pyrazoles via [3+2] annulation reaction between hydrazones and cyclic enones (five-, six- and seven-membered) catalyzed by Cu(II) under aerobic conditions. These compounds were further functionalized by reactions such as Suzuki-Miyaura cross-coupling, Heck coupling, and Aldol reaction to afford diverse molecular scaffolds in good yield, selectivity and functional group tolerance. © 2023 Wiley-VCH GmbH.
Synthesis of 5-(pyrazol-4-yl) pentanoic acids and 4-(pyrazol-4-yl) butanoic acids via a cascade annulation/ring-opening reaction between hydrazone and dienone
(Royal Society of Chemistry, 2025) Nayak, K.H.; Jijin, R.K.; Babu, B.P.
Herein, we report an interesting [3 + 2] annulation/ring-opening cascade reaction between hydrazones and exocyclic dienones via an aerobic, copper(ii) catalysis to synthesize 5-(pyrazol-4-yl) pentanoic acid and 4-(pyrazol-4-yl) butanoic acid derivatives. The annulation first affords a spiro pyrazoline with unprecedented regiochemistry, followed by a cascade nucleophilic ring opening by water to yield pyrazolyl pentanoic and butanoic acid derivatives in good yield. Broad substrate scope, inexpensive and green catalyst and oxidant, and relatively mild reaction conditions enhance the versatility of this protocol. © 2025 The Royal Society of Chemistry.
Synthesis of functionalized benzo[1,3]dioxin-4-ones from salicylic acid and acetylenic esters and their direct amidation
(Royal Society of Chemistry, 2021) Bhaskaran, R.P.; Nayak, K.H.; Babu, B.P.
Direct synthesis of 4H-benzo[d][1,3]dioxin-4-one derivatives from salicylic acids and acetylenic esters (both mono- and disubstituted) has been described. The reaction is mediated by CuI and NaHCO3in acetonitrile. Room temperature amidation of the synthesized 1,3-benzodioxinones with primary amines readily afforded the corresponding salicylamides in moderate to good yields. © The Royal Society of Chemistry 2021.