Now showing 1 - 10 of 65
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    Synthesis of Chiral 1,2-Oxazinanes and isoxazolidines via nitroso aldol reaction of distal dialdehydes
    (16-02-2018)
    Ramakrishna, Isai
    ;
    Ramaraju, Panduga
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    The first catalytic enantioselective nitroso aldol reaction of distal dialdehydes is reported. The reaction is catalyzed by simple l-proline at room temperature and subsequent reduction delivered biologically potent and synthetically versatile N-O bond containing five- and six-membered heterocycles, 1,2-oxazinanes, and isoxazolidines in high yields and excellent enantioselectivities (up to >99% ee). The method was further exploited to prepare chiral 3-hydroxypiperidines and -pyrrolidines that are otherwise difficult to access.
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    Catalytic Regiodivergent Dearomatization Reaction of Nitrosocarbonyl Intermediates with β-Naphthols
    (05-04-2019)
    Mallik, Sumitava
    ;
    Bhajammanavar, Vinod
    ;
    Mukherjee, Arka Probha
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    The divergent reactivity of nitrosocarbonyls in oxidative dearomatization of β-naphthols is reported. In the presence of quinidine catalyst, their reactions with α-unsubstituted β-naphthols proceeded through the N-center to furnish α-imino-β-naphthalenones in high yields. Upon exposure to α-substituted β-naphthols in the presence of copper catalyst, an alteration of regioselectivity was observed to produce α-aminoxylation products. The reaction is scalable, tolerates a wide spectrum of functional groups, and represents a rare example of dearomatization of α-unsubstituted β-naphthols.
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    Catalyst-Controlled Regioselective Nitrosocarbonyl Aldol Reaction of Deconjugated Butenolides
    (21-02-2020)
    Mallik, Sumitava
    ;
    Bhajammanavar, Vinod
    ;
    An unprecedented regiodivergent nitrosocarbonyl aldol reaction of γ-substituted deconjugated butenolides is described. While Lewis base catalyst quinidine leveraged O-selective nitrosocarbonyl aldol reaction exclusively at the γ-position of deconjugated butenolides to produce γ-aminoxylation products, Lewis acid catalyst Cu(OTf)2 steered the competitive N-selective nitrosocarbonyl aldol reaction at the β-position, resulting in heterodifunctionalized butenolides. Both processes were amenable to a broad range of substrates and scalable, while the latter one represents a rare example of one-pot hetero-β,γ-difunctionalization of butenolide scaffolds.
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    Radical Cascade Reaction of Aryl Alkynoates at Room Temperature: Synthesis of Fully Substituted α,β-Unsaturated Acids with Chalcogen Functionality
    (15-06-2018)
    Sahoo, Harekrishna
    ;
    Singh, Saibal
    ;
    A radical-based cascade reaction has been devised for oxidative difunctionalization of aryl alkynoates at room temperature to access stereodefined fully substituted α,β-unsaturated acids bearing a chalcogen functionality in high yields (up to 95%). The protocol is operationally simple, metal-free, scalable, and suppresses the usual CO2 exclusion phenomenon. The utility of this method was showcased in the synthesis of vinyl halides, vinyl selenides, and 3,3-disubstituted indanones.
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    Regio- and Stereoselective Allylation of Anilines with Aryl Allenes in Hexafluoroisopropanol Solvent
    (14-07-2023)
    Ghosh, Suman
    ;
    Saha, Shib Nath
    ;
    A regio- and stereoselective allylation of N-unsubstituted anilines has been developed that explores aryl allenes as masked allyl synthons and a combination of Mg(OTf)2/HFIP as an effective proton source. The protocol is operationally simple and scalable and offers high yields of diverse p-allyl anilines bearing an olefin motif with exclusive E-geometry. The methodology was also suitable for the regioselective allylation of indole and can be advanced in a three-component reaction mode using NIS activator. The alteration of the catalytic system with TfOH resulted in the regioselective difunctionalization of allenes, which follows an allylation/hydroarylation cascade.
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    Ruthenium(II) Catalysis/Noncovalent Interaction Synergy for Cross-Dehydrogenative Coupling of Arene Carboxylic Acids
    (02-11-2018)
    Dana, Suman
    ;
    Chowdhury, Deepan
    ;
    Mandal, Anup
    ;
    Chipem, Francis A.S.
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    A ruthenium-catalyzed cross-dehydrogenative coupling is developed with the aid of a weakly coordinating carboxylic acid group toward the dimerization of arene carboxylic acids. The protocol is operationally simple and suitable to fabricate diverse homodimerized as well as cross-dimerized products in high yields. Computational insights have also been unveiled to comprehend the plausible reaction mechanism. The critical innovation of the synthetic strategy hinges on the soluble basic additive DBU, which constitutes a synergy of Ru(II)-catalysis with noncovalent interaction and, thus, stabilizes pivotal intermediates to promote the challenging dimerization process.
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    Diastereoselective access to [4,4]-carbospirocycles: governance of thermodynamic enolates with an organocatalyst in vinylogous cascade annulation
    (14-02-2022)
    Bhajammanavar, Vinod
    ;
    Mallik, Sumitava
    ;
    Choutipalli, Venkata Surya Kumar
    ;
    Subramanian, Venkatesan
    ;
    A vinylogy concept driven annulation strategy is developed to access [4,4]-carbospirocycles from alkylidene malononitriles and cyclopentene-1,3-diones. The reaction is catalyzed by an inexpensive organocatalyst and products with three stereocenters were obtained as a single diastereomer in high yields. The spiro-selectivity originates from the reaction of the thermodynamic enolate intermediate which is fundamentally intriguing.
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    Copper-Catalyzed 8-Amido Chelation-Induced Remote C-H Amination of Quinolines
    (26-01-2016)
    Sahoo, Harekrishna
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    Reddy, Mallu Kesava
    ;
    Ramakrishna, Isai
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    A copper-catalyzed 8-amide chelation-induced remote C-H amination of quinolines has been developed. This direct amination with readily available azodicarboxylates proceeded with perfect C5-regioselectivity offering amino-substituted 8-aminoquinolines, important bioactive molecular scaffolds, in very high yields (up to 96 %). A single-electron transfer (SET)-mediated mechanism with kH/kD=1.1 was proposed after trapping of the radical intermediate. Access the inaccessible: A copper-catalyzed 8-amide chelation-induced remote C-H amination of quinolines has been developed (see scheme). This direct amination with readily available azodicarboxylates proceeded with perfect C5-regioselectivity offering amino-substituted 8-aminoquinolines in high yields (up to 96 %).
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    Cross-Dehydrogenative Coupling/Annulation of Arene Carboxylic Acids and Alkenes in Water with Ruthenium(II) Catalyst and Air
    (01-12-2020)
    Mandal, Anup
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    Garai, Bholanath
    ;
    Dana, Suman
    ;
    Bera, Ratnadeep
    ;
    A cross-dehydrogenative coupling of arene carboxylic acids with olefins is reported with ruthenium(II) catalyst employing air and water as green oxidant and solvent, respectively. It offers a robust synthesis of valuable phthalide molecules. A one-pot sequential strategy is also disclosed to access Heck-type products that are apparently difficult to make directly from arene carboxylic acids.
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    Divergent Reaction of Activated Pyridines with α,α-Difluorinated gem-Diols: Regioselective Synthesis of gem-Difluorinated Dihydropyridines and Dihydropyridones
    (10-06-2022)
    Patra, Koushik
    ;
    Reddy, Mallu Kesava
    ;
    Mallik, Sumitava
    ;
    The nucleophilic reactivity of α,α-difluorinated gem-diols toward activated pyridinium salts has been capitalized in a highly regioselective fashion, offering biologically relevant 1,4-dihydropyridines and 3,4-dihydro-2-pyridones adorned with the valuable gem-difluoromethylene motif. The protocol is scalable as well as high yielding and accommodates a broad range of substrates and functional groups. Additionally, the synthesis of difluorinated oxa-azabicyclo[3.3.1]nonane frameworks has been showcased through product diversification.