Browsing by Author "Sreelekha, M.K."

Filter results by typing the first few letters
Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    In Situ Generation and [3 + 2] Annulation Reactions of Propiolaldehyde?A Metal-Free, Cascade Route to Pyrazole and Bipyrazole Carboxaldehydes in One Pot
    (American Chemical Society, 2025) Sreelekha, M.K.; Shamnad, A.; Bhaskaran, R.P.; Babu, B.P.
    Propiolaldehyde, the most reactive yet less explored electrophilic acetylene, was generated in situ via a base-free Kornblum oxidation from propargyl tosylate and successfully intercepted with hydrazones affording pyrazole-4-carboxaldehyde in one-pot by a [3 + 2] annulation reaction. Further, the pyrazole-4-carboxaldehyde endured a unique cascade reaction with phenylhydrazine and propargyl tosylate, yielding synthetically challenging bipyrazole carboxaldehydes. The method is free of any metal catalyst, base, or additives and offers a convenient protocol to handle the reactive and volatile propiolaldehyde under ambient conditions. © 2025 American Chemical Society.
  • No Thumbnail Available
    Item
    Metal-free Synthesis of Trisubstituted Pyrazoles by the Reaction Between Hydrazones and Activated Olefins
    (John Wiley and Sons Inc, 2022) Bhaskaran, R.P.; Sreelekha, M.K.; Babu, B.P.
    The reactivity of various activated olefins towards the [3+2] annulation with hydrazones (aza-enamines) has been studied. Nitroolefins, methyl vinyl ketone, acrylates and acrylamide were found to react with aldehyde hydrazones of different electronic nature to generate 1,3,5-/1,3,4–trisubstituted pyrazoles selectively. A detailed optimization study was conducted to derive the best condition for the annulation reaction of different olefin partner and the intermediate dihydropyrazole is also identified. © 2022 Wiley-VCH GmbH.
  • No Thumbnail Available
    Item
    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.