Browsing by Author "Dharmendra Kumar Tiwari"

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A three-component, general and practical route for diastereoselective synthesis of aza-spirocyclic pyrazolonesviaa decarboxylative annulation process
(Royal Society of Chemistry, 2021) Annapurna Awasthi; Pushpendra Yadav; Dharmendra Kumar Tiwari
An efficient, general, and practical route for highly diastereoselective synthesis of aza-spirocyclic pyrazolones from easily available α-amino acids, aldehydes, and alkylidene pyrazolones by means of a decarboxylative annulation process is reported. This high-yielding reaction proceeds through a [3+2]-cycloaddition reaction between alkylidene pyrazolones and a nonstabilized azomethine ylide generatedin situ. This method provides easy and smooth access to a variety of highly functionalized aza-spirocyclic pyrazolones in excellent yields (up to 96%). The obtained spiro-pyrazolones comprise four contiguous stereogenic centers including a quaternary carbon center. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2021.
Autocatalytic and DMSO-promoted regioselective synthesis of pyrimidine-fused quinolines from anilines and barbituric acids
(Royal Society of Chemistry, 2024) Pushpendra Yadav; Deblina Chatterjee; Suman Bhowmick; Khushboo Tiwari; Annapurna Awasthi; Dharmendra Kumar Tiwari
Autocatalytic and DMSO-participating regioselective synthesis of N,N-disubstituted pyrimido[4,5-b]quinoline-2,4(1H,3H)-diones from anilines and barbituric acids has been achieved. In this newly developed one-pot tandem reaction, DMSO serves as a solvent cum methine source. Additionally, barbituric acid plays a dual role by acting as a substrate and a catalyst, making this reaction an environmentally benign approach to accessing valuable heterocycles. This method offers an auto-catalytic, additive-free, and operationally simple approach with a wide substrate scope and excellent tolerance for various functional groups. Furthermore, a few controlled experiments were conducted to gain insight into the reaction mechanism. Moreover, large-scale experiments have further enriched this methodology. © 2024 The Royal Society of Chemistry.
Copper Catalyzed Synthesis of 3-Nitro-Quinolines from Nitro-Olefins and Anthranils: Its Application in the Synthesis of Quindoline
(John Wiley and Sons Inc, 2022) Annapurna Awasthi; Pushpendra Yadav; Sourabh Yadav; Dharmendra Kumar Tiwari
Copper-catalyzed routes have been achieved for the synthesis of 3-nitroquinolines from readily available nitroolefins and anthranils. This reaction proceeds via the [4+2] cycloaddition between anthranils and nitro-styrenes under mild reaction conditions to obtain biologically important heterocycles. A wide range of diversely substituted nitro-olefins and anthranils are successfully employed in this reaction to access a series of 3-nitro-quinolines in 81–93% yields. The synthetic utility of the present methodology is also illustrated in this manuscript. (Figure presented.). © 2021 Wiley-VCH GmbH
DMSO as a dual carbon synthon in one-pot tandem synthesis of N-alkylated quinazolinones from anthranilamides and acetophenones
(Royal Society of Chemistry, 2022) Pushpendra Yadav; Sourabh Yadav; Annapurna Awasthi; Mandalparthi Phanindrudu; Suman Bhowmick; Dharmendra Kumar Tiwari
A new, efficient, metal-free, and DMSO-assisted approach for the synthesis of N-alkylated quinazolinones from readily available 2-aminobenzamide and aryl methyl ketones in the presence of an oxidizing agent has been developed. In this unique tandem reaction, DMSO played a dual role, acting as a solvent as well as a dual carbon synthon, making this process an environmentally benign approach to accessing medicinally prevalent N-alkylated quinazolinones. The DMSO-assisted in situ generation of an iminium cation and α,β-unsaturated ketones from 2-aminobenzamide and aryl methyl ketones, respectively, is the key feature involved in this method. © 2022 The Royal Society of Chemistry.
DMSO as a Methine Source in TFA-Mediated One-Pot Tandem Regioselective Synthesis of 3-Substituted-1-Aryl-1 H-Pyrazolo-[3,4- b]quinolines from Anilines and Pyrazolones
(American Chemical Society, 2021) Pushpendra Yadav; Annapurna Awasthi; Sabapathi Gokulnath; Dharmendra Kumar Tiwari
An acid-mediated and DMSO participant one-pot tandem synthesis of 3-substituted-1-aryl-1H-pyrazolo-[3,4- b]quinoline from readily available anilines and pyrazolones was achieved. This method enables regioselective construction of the valuable heterocycles under transition-metal and oxidant-free conditions in which DMSO acts as a methine source as well as solvent making this process an environmentally benign approach. A broad range of diversely substituted aryl amines and pyrazolines are successfully employed in this reaction to access a series of pyrazolo[4,3-c]quinolones through a novel cascade mechanism. Furthermore, the application and mechanistic studies of the present methodology also demonstrated. ©
Double Morita-Baylis-Hillman (MBH) strategy; An intermolecular and a chemo selective intramolecular MBH reactions for 5/6 substituted, functionalized piperidine unit
(Elsevier Ltd, 2016) Kishor Chandra Bharadwaj; Dharmendra Kumar Tiwari
A novel approach utilizing dual Morita-Baylis-Hillman (MBH) reactions in form of intermolecular and a chemo selective intramolecular version, has been developed. With three electrophilic and a nucleophilic site in precursor, selective condition for intramolecular MBH reaction has been optimized. Role of water was found to be crucial. The dual strategy was applicable for synthesis of a variety of medicinally and synthetically important piperidine unit whose 5/6 atoms of ring were substituted, featuring a stereo defined trisubstituted olefin, a Michael acceptor (with a methylene moiety), trivalent nitrogen and a tertiary alcohol. © 2015 Elsevier Ltd. All rights reserved.
Magnetically Recoverable Cu0/Fe3O4-Catalysed One-Pot Tandem Synthesis of Sulfur-Containing Triazoles from Alkynes and Azide: DMSO Acts as an Alkylating Agent
(Wiley-VCH Verlag, 2016) Mandalaparthi Phanindrudu; Dipak Kumar Tiwari; Vinod Kumar Aravilli; Kishor Chandra Bhardwaj; Gokulnath Sabapathi; Pravin R. Likhar; Dharmendra Kumar Tiwari
An efficient one-pot tandem nano Cu0/Fe3O4-catalysed synthesis of sulfur-containing triazoles from alkynes and azide has been developed. In this newly developed method, the readily available TMS-azide and dimethyl sulfoxide act as nitrogen and sulfur sources, respectively. The catalyst was magnetically recovered and reused six times without any significant loss of activity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Morita-Baylis-Hillman reaction of acrylamide with isatin derivatives
(Beilstein-Institut Zur Forderung der Chemischen Wissenschaften, 2014) Radhey M. Singh; Kishor Chandra Bharadwaj; Dharmendra Kumar Tiwari
The Morita-Baylis-Hillman reaction of acrylamide, as an activated alkene, has seen little development due to its low reactivity. We have developed the reaction using isatin derivatives with acrylamide, DABCO as a promoter and phenol as an additive in acetonitrile. The corresponding aza version with acrylate and acrylonitrile has also been developed resulting in high product yields. © 2014 Singh et al; licensee Beilstein-Institut. License and terms: see end of document.
Rhenium-Catalyzed C(sp2)-H Silylalkenylation of Arenes: An Anti-Markovnikov Linchpin Strategy
(American Chemical Society, 2025) Suman Bhowmick; Annapurna Awasthi; Khushboo Tiwari; Pushpendra Yadav; Dharmendra Kumar Tiwari
Re-catalyzed highly regio- and stereoselective o-C(sp2)-H silylalkenylation of arenes is reported using a directing group approach under ligand-, additive-, and base-free conditions. A series of imine directing groups (DGs) have been exploited on aromatic aldehydes to overcome de novo synthesis. This unique protocol allows us to access o-C-H activation of various heterocyclic moieties, including N-aryl 2-pyridones and arylpyridines. Sequential difunctionalization experiments have been performed. A series of mechanistic experiments have been carried out to gain mechanistic insight. © 2025 American Chemical Society.
Synthesis of 4-styrylquinolines via direct oxidative C3-alkenylation of anthranils under Pd(ii) catalysis
(Royal Society of Chemistry, 2024) Annapurna Awasthi; Khushboo Tiwari; Pushpendra Yadav; Suman Bhowmick; Dharmendra Kumar Tiwari
The palladium-catalyzed oxidative C3-alkenylation of anthranils (2,1-benzisoxazoles) with various styrenes has been successfully achieved. The C3-alkenylated anthranils were subsequently utilized in a [4+2]-cycloaddition with in situ generated α,β-unsaturated ketones leading to the synthesis of a diverse range of olefin-containing quinolines. Notably, this reaction exclusively yielded mono-alkenylated products with E-selectivity. The optimized catalytic conditions were compatible with a wide variety of substituted olefins and anthranils, forming various C3-alkenylated anthranils with good yields. To showcase the application of the present methodology, the C3-alkenylated anthranils have been employed as synthons to access a wide range of substituted quinolines. © 2024 The Royal Society of Chemistry.
Tf2O-mediated [4+2]-annulation of anthranils with 2-chloropyridines: enabling access to pyridoquinazolinones and euxylophoricine B
(Royal Society of Chemistry, 2024) Annapurna Awasthi; Khushboo Tiwari; Dharmendra Kumar Tiwari
We present an efficient approach for synthesizing pyridoquinazolinones in the presence of triflic anhydride utilizing anthranils and 2-chloropyridines as starting materials. In this process, Tf2O initially activates anthranils forming an electrophilic 1-((trifluoromethyl)sulfonyl)benzo[c]isoxazol-1-ium species. This species undergoes an in situ annulation reaction with 2-chloropyridines, resulting in therapeutically useful pyridoquinazolinones. The reaction is tolerant to various functional groups, allowing access to a wide range of substituted pyridoquinazolinones in good yields. Furthermore, the synthesis of euxylophoricine B, known to be an antitumor agent, was also achieved. © 2024 The Royal Society of Chemistry.
α-Amino Acids Mediated C−C Double Bonds Cleavage in Diastereoselective Synthesis of Aza-Spirocyclic Pyrazolones
(Wiley-VCH Verlag, 2020) Annapurna Awasthi; Pushpendra Yadav; Virendra Kumar; Dharmendra Kumar Tiwari
An efficient and reagent-free synthesis of highly functionalized aza-spirocyclic pyrazolones are achieved from easily available α-amino acids and alkylidene pyrazolones by means of amination, C−C-double bonds cleavage, and decarboxylative annulation process. These highly diastereoselective reactions are promoted simply by α-amino acids and involve in situ generated azomethine ylides as reactive intermediates. This newly developed protocol involves the formation of three new bonds (one C−N and two C−C) and four new contiguous stereo-centers including a quaternary carbon center in a single pot cascade process. (Figure presented.). © 2020 Wiley-VCH GmbH