Browsing by Author "Babu, B.P."

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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.
Functionalizable 1H-Indazoles by Palladium Catalyzed Aza-Nenitzescu Reaction: Pharmacophores to Donor-Acceptor Type Multi-Luminescent Fluorophores
(2018) Janardhanan, J.C.; Mishra, R.K.; Das, G.; Sini, S.; Jayamurthy, P.; Suresh, C.H.; Praveen, V.K.; Manoj, N.; Babu, B.P.
Development of small-molecule-based multi-luminescent fluorophores utilizing simple synthetic methodologies, as well as easily available starting materials, has gained much attention in recent years. Herein, we disclose an efficient protocol for the synthesis of N-protected 1H-indazole derivatives with diverse substituents at their 3- and 5-positions via palladium-catalyzed reactions of hydrazones and p-benzoquinones. The obtained 1H-indazole derivatives can be easily modified into donor-acceptor (D?A)-type chromophores (Indazo-Fluors) with tunable emission properties in both solid and solution state. Owing to the extent of intramolecular charge transfer, Indazo-Fluors exhibit positive solvatochromic emission spanning from blue-green to orange-red. Theoretical studies were undertaken to rationalize the observed trends in the optical properties of Indazo-Fluors. Finally, a triethylene glycol (TEG) appended Indazo-Fluor exhibiting a large Stokes shift and low cytotoxicity allowed us to use it for cell imaging. 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Functionalizable 1H-Indazoles by Palladium Catalyzed Aza-Nenitzescu Reaction: Pharmacophores to Donor-Acceptor Type Multi-Luminescent Fluorophores
(Wiley-VCH Verlag info@wiley-vch.de, 2018) Janardhanan, J.C.; Mishra, R.K.; Das, G.; Sini, S.; Jayamurthy, P.; Suresh, C.H.; Praveen, V.K.; Manoj, N.; Babu, B.P.
Development of small-molecule-based multi-luminescent fluorophores utilizing simple synthetic methodologies, as well as easily available starting materials, has gained much attention in recent years. Herein, we disclose an efficient protocol for the synthesis of N-protected 1H-indazole derivatives with diverse substituents at their 3- and 5-positions via palladium-catalyzed reactions of hydrazones and p-benzoquinones. The obtained 1H-indazole derivatives can be easily modified into donor-acceptor (D?A)-type chromophores (Indazo-Fluors) with tunable emission properties in both solid and solution state. Owing to the extent of intramolecular charge transfer, Indazo-Fluors exhibit positive solvatochromic emission spanning from blue-green to orange-red. Theoretical studies were undertaken to rationalize the observed trends in the optical properties of Indazo-Fluors. Finally, a triethylene glycol (TEG) appended Indazo-Fluor exhibiting a large Stokes shift and low cytotoxicity allowed us to use it for cell imaging. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Green Chemistry of Recoverable Catalysts
(Springer Nature, 2021) Bhaskaran, R.P.; Babu, B.P.
This chapter highlights the various aspects of recoverable catalysts, a green concept. Catalysts play a vital role in the chemical and pharmaceutical industries. Environmental considerations aim toward its recycling and reuse. Recovery of the catalyst after the reaction and its reuse focuses on the sustainable greener approaches in chemical industries. The question is, how effectively the catalyst recovery can be achieved. To address the issue of catalyst regeneration, scientists have developed a wide range of strategies. One approach to classify the catalysts is based on their method of separation, and the majority comes under heterogenized solid-supported catalysts. In this context, the development of new logical solutions for the regeneration and reuse of the catalysts without losing the activity is of prime importance. © 2021, Springer Nature Singapore Pte Ltd.
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.
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
Metal-Free Synthesis of Pyrazoles and Chromenopyrazoles from Hydrazones and Acetylenic Esters
(Wiley-Blackwell info@wiley.com, 2020) Bhaskaran, R.P.; Janardhanan, J.C.; Babu, B.P.
An efficient, metal-free synthesis of pyrazoles and chromenopyrazoles from aldehyde hydrazones and acetylenic esters has been developed. A library of molecules with diverse functional groups has been synthesized using substituted hydrazones and alkynes, both symmetrical and unsymmetrical ones. The derivatives were isolated in moderate to good yields. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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.
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.
Progress in Electrochemical Trifluoromethylation Reactions
(Wiley-VCH Verlag, 2020) Bhaskaran, R.P.; Babu, B.P.
The importance of fluorinated organic molecules in drugs and pharmaceuticals led to the development of several synthetic methods for introducing fluorine into bioactive molecules and trifluoromethylation is one of the key approaches for the same. Electrochemical organic synthesis has emerged as one of the most sustainable, green synthetic strategies in recent years and new developments in electroorganic synthesis also focus on electrochemical trifluoromethylation of organic compounds. A considerable number of reports have appeared in recent literature and this review surveys all the recent developments in electrochemical trifluoromethylation reactions. This highly sustainable trifluoromethylating protocol will emerge further soon and pave the way for more energy-efficient and green protocols. (Figure presented.). © 2020 Wiley-VCH GmbH
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.
Synthesis of hybrid polycycles containing fused hydroxy benzofuran and 1H-indazoles via a domino cyclization reaction
(2019) Janardhanan, J.C.; James, K.; Puthuvakkal, A.; Bhaskaran, R.P.; Suresh, C.H.; Praveen, V.K.; Manoj, N.; Babu, B.P.
A stoichiometry controlled domino cyclization reaction of hydrazone and p-benzoquinone to an angularly fused 3H-benzofuro[3,2-e]indazole core with an embedded oxygenated dibenzofuran framework under mild reaction conditions is disclosed. The reaction involves palladium catalyzed 5-hydroxy-1H-indazole formation followed by TFA mediated [3+2] annulation between the in situ formed 5-hydroxy-1H-indazole and p-benzoquinone. The developed method is attractive because of the concomitant formation of two heterocyclic rings with consecutive multiple bond forming events that include two C-C, one C-N and one C-O bonds. Spectroscopic and theoretical studies of the blue emissive benzofuroindazole derivatives have also been described. 2019 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Synthesis of hybrid polycycles containing fused hydroxy benzofuran and 1H-indazoles via a domino cyclization reaction
(Royal Society of Chemistry, 2019) Janardhanan, J.C.; James, K.; Puthuvakkal, A.; Bhaskaran, R.P.; Suresh, C.H.; Praveen, V.K.; Manoj, N.; Babu, B.P.
A stoichiometry controlled domino cyclization reaction of hydrazone and p-benzoquinone to an angularly fused 3H-benzofuro[3,2-e]indazole core with an embedded oxygenated dibenzofuran framework under mild reaction conditions is disclosed. The reaction involves palladium catalyzed 5-hydroxy-1H-indazole formation followed by TFA mediated [3+2] annulation between the in situ formed 5-hydroxy-1H-indazole and p-benzoquinone. The developed method is attractive because of the concomitant formation of two heterocyclic rings with consecutive multiple bond forming events that include two C-C, one C-N and one C-O bonds. Spectroscopic and theoretical studies of the blue emissive benzofuroindazole derivatives have also been described. © 2019 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Transition-Metal-Catalyzed Syntheses of Indazoles
(Wiley-VCH Verlag info@wiley-vch.de, 2020) Janardhanan, J.C.; Bhaskaran, R.P.; Praveen, V.K.; Manoj, N.; Babu, B.P.
Indazole is an important heterocyclic scaffold exhibiting a wide range of biological and pharmacological properties and plays a crucial role in drug design. In recent years, indazoles have gained attention in materials chemistry owing to their promising photophysical properties. The biomedical importance and natural rarity inspire the development of new practical syntheses of the indazole core. In this review, we are presenting a comprehensive overview of recent developments in the transition metal-catalyzed synthesis of indazole during the last decade. © 2020 Wiley-VCH GmbH