Browsing by Author "Gaurav Shukla"

Now showing 1 - 20 of 52

4-Dimethylamino pyridine-promoted one-pot three-component regioselective synthesis of highly functionalized 4 H -thiopyrans via heteroannulation of β-oxodithioesters
(2012) Rajiv Kumar Verma; Girijesh Kumar Verma; Gaurav Shukla; Anugula Nagaraju; Maya Shankar Singh
A highly convergent and regioselective heteroannulation protocol for the synthesis of hitherto unreported highly substituted 2-amino-4-(aryl/alkyl)-5- (aroyl/heteroaroyl)-3-(cyano/carboalkoxy)-6-methylthio-4H-thiopyran derivatives has been developed. This one-pot three-component domino coupling of β-oxodithioesters, aldehydes, and malononitrile/ethyl or methyl cyanoacetate is promoted by 4-dimethylamino pyridine (DMAP) in solvent (dichloromethane (DCM)) as well as under solvent-free conditions. Systematic optimization of reaction parameters identified that the three-component coupling (3CC) protocol is tolerant to a wide array of functionality providing densely functionalized 4H-thiopyrans in excellent yields. The merit of this cascade Knoevenagel condensation/Michael addition/cyclization sequence is highlighted by its high atom-economy, excellent yields, and efficiency of producing three new bonds (two C-C and one C-S) and one stereocenter in a single operation. © 2012 American Chemical Society.
A facile and highly convergent approach to thiazolo[3,2-a]pyridines via one-pot multicomponent domino reaction under metal-free and solvent-free conditions
(Elsevier Ltd, 2015) Anugula Nagaraju; B. Janaki Ramulu; Gaurav Shukla; Abhijeet Srivastava; Girijesh Kumar Verma; Keshav Raghuvanshi; Maya Shankar Singh
Abstract Operationally and user-simple a highly efficient one-pot three-component (5 molecules) coupling of α-enolic dithioesters, cysteamine hydrochloride and aldehydes afforded a range of thiazolopyridines in high yields under metal-free and solvent-free conditions. The new domino protocol generated two rings by the concomitant formation of seven multiple bonds (two C-C, three C-N and two C-S) involving a sequence of N,S-acetal formation/double Michael addition/N-cyclization as key steps in a single operation. © 2015 Elsevier Ltd. All rights reserved.
A facile and straightforward synthesis of 1,2,3-thiadiazoles from α-enolicdithioesters via nitrosation/reduction/diazotization/cyclization cascade in one-pot
(Elsevier Ltd, 2014) Anugula Nagaraju; B. Janaki Ramulu; Gaurav Shukla; Abhijeet Srivastava; Girijesh Kumar Verma; Keshav Raghuvanshi; Maya Shankar Singh
An operationally simple, economical, and straightforward synthesis of diverse 4,5-disubstituted 1,2,3-thiadiazoles from α-enolicdithioesters has been achieved via nitrosation/reduction/diazotization/cyclization sequence in one-pot through the formation of cascade 1-2 (N-S) and 3-4 (C-N) bonds. Importantly, this is the first straightforward entry to highly functionalized 1,2,3-thiadiazoles from dithioesters. © 2014 Elsevier Ltd. All rights reserved.
Access to Fully Substituted Thiazoles and 2,3-Dihydrothiazoles via Copper-Catalyzed [4 + 1] Heterocyclization of α-(N-Hydroxy/aryl)imino-β-oxodithioesters with α-Diazocarbonyls
(American Chemical Society, 2017) Abhijeet Srivastava; Gaurav Shukla; Dhananjay Yadav; Maya Shankar Singh
An efficient chemoselective practical route to fully substituted thiazoles and 2,3-dihydrothiazoles has been devised by [4 + 1] heterocyclization of α-(N-hydroxy/aryl)imino-β-oxodithioesters with in situ generated Cu-carbenoids of diazocarbonyls. The α-(N-hydroxy/aryl)imino-β-oxodithioesters are readily accessible by the reaction of β-oxodithioesters with nitrous acid/nitrosoarenes. The overall transformation involves sequential N-O/C-N bonds cleavage followed by cascade C-N/C-S bonds formation in one-pot. This new strategy allows full control over the introduction of various sensitive functional groups at different positions of the thiazole ring, broadening the arsenal of synthetic methods to obtain such scaffolds. © 2017 American Chemical Society.
Access to Nitrones from Amines via Electrocatalysis at Room Temperature
(John Wiley and Sons Inc, 2022) Gaurav Shukla; Dhananjay Yadav; Saurabh Singh; Maya Shankar Singh
A self-enabled electrooxidative protocol for the synthesis of nitrones from bench stable amines has been developed under constant current electrolysis at room temperature, rendering metal and external oxidant-free protocol in an alkaline medium. The electrocatalysis steps of reported strategy involve anodic oxidation of benzyl amines followed by cathodic reduction of nitro-functional group in an undivided cell affording functional nitrones. The robustness of the electrocatalysis was reflected by tolerant substrate scope, oxidant-free conditions, and an operationally friendly procedure. Moreover, the cyclic voltammetry and control experiment studies also support the electrochemical process in alkaline medium. (Figure presented.). © 2022 Wiley-VCH GmbH.
Annulative Coupling of Tetrahydroisoquinolines with Aryliodonio diazo compounds to Access 1,2,4-Triazolo[3,4- a]isoquinolines
(American Chemical Society, 2022) Monish Arbaz Ansari; Shahnawaz Khan; Subhasish Ray; Gaurav Shukla; Maya Shankar Singh
Base promoted one-pot annulative coupling of 1,2,3,4-tetrahydroisoquinolines (THIQs) with hypervalent iodine(III) species aryliodonio diazo compounds has been devised for the direct construction of 1,2,4-triazolo[3,4-a]isoquinoline derivatives at room temperature in open air for the first time. This approach involves [2 + 3] cascade annulation of nucleophilic THIQ with an electrophilic aryliodonio diazo compound via N-H and α-C1(sp3)-H difunctionalization of THIQ. © 2022 American Chemical Society. All rights reserved.
Aromatic C(sp2)−H Functionalization by Consecutive Paired Electrolysis: Dibromination of Aryl Amines with Dibromoethane at Room Temperature
(John Wiley and Sons Inc, 2024) Gaurav Shukla; Malkeet Singh; Anup Kumar Yadav; Maya Shankar Singh
Herein, we disclose a facile and efficient electrochemical method for the dibromination of aryl amines by double functionalization of aromatic C(sp2)−H (both para and ortho) under metal- and external oxidant-free conditions at room temperature for the first time. The reaction is demonstrated using 1,2-dibromoethane to dibrominate a wide range of N-substituted aryl amines in a simple setup with C(+)/Pt(−) electrodes under mild reaction conditions. This transformation proceeds smoothly with a broad substrate scope affording the valuable and versatile N-substituted 2,4-dibromoanilines in moderate to excellent yields with high regioselectivity. In this paired electrolysis, cathodic reduction of 1,2-DBE followed by anodic oxidation generates bromonium intermediates, which then couple with anilines to furnish the dibrominated products. It represents a distinctive approach to challenging redox-neutral reactions. The versatility of the electrochemical ortho-, para-dibromination was reflected by unique regioselectivities for challenging aryl amines and gram-scale electrosynthesis without the use of a stoichiometric oxidant or an activating agent. © 2023 Wiley-VCH GmbH.
Broadening the high sensitivity range of squeezing-assisted interferometers by means of two-channel detection
(OSA - The Optical Society, 2021) Gaurav Shukla; Dariya Salykina; Gaetano Frascella; Devendra Kumar Mishra; Maria V. Chekhova; Farit Ya. Khalili
For a squeezing-enhanced linear (so-called SU(2)) interferometer, we theoretically investigate the possibility to broaden the phase range of sub-shot-noise sensitivity. We show that this goal can be achieved by implementing detection in both output ports, with the optimal combination of the detectors outputs. With this modification, the interferometer has the phase sensitivity independent of the interferometer operation point and, similar to the standard dark port regime, is not affected by the laser technical (excess) noise. Provided that each detector is preceded by a phase-sensitive amplifier, this sensitivity could be also tolerant to the detection loss. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.
Brønsted acid-catalyzed metal-free one-pot synthesis of benzimidazoles via [4+1] heteroannulation of ortho-phenylenediamines with β-oxodithioesters
(Arkat, 2017) Abhijeet Srivastava; Gaurav Shukla; Dhananjay Yadav; Maya Shankar Singh
An operationally simple and user-friendly one-pot domino protocol for the synthesis of 2-aryl/hetaryl benzimidazoles has been devised from easily available and inexpensive 1,2-phenylenediamines and β-oxodithioesters. The strategic [4+1] heteroannulation initiated by Bronsted acid PTSA relies on remarkable domino sequence of condensation, cyclization, and elimination. The current approach enables N-H/N-H functionalization under solventless and metal-free conditions leading to diverse benzimidazoles. The reactions proceeded smoothly affording the desired products in good to excellent yields, exhibiting gram-scale ability and broad functional groups tolerance. Notably, the approach is highly chemo- and regioselective. © 2018 ARKAT USA, Inc.
Catalyst-free one-pot four-component domino reactions in water-PEG-400: Highly efficient and convergent approach to thiazoloquinoline scaffolds
(Royal Society of Chemistry, 2015) Anugula Nagaraju; B. Janaki Ramulu; Gaurav Shukla; Abhijeet Srivastava; Girijesh Kumar Verma; Keshav Raghuvanshi; Maya Shankar Singh
A cost-effective and eco-friendly straightforward synthesis of highly diversified thiazoloquinoline scaffolds is successfully achieved via one-pot four-component cascade reaction utilizing α-enolic dithioesters, cysteamine, aldehydes, and cyclic 1,3-diketones in water-PEG-400. The new efficient domino protocol generates two rings by the concomitant formation of C-C (two), C-N (two), and C-S multiple bonds presumably involving a sequence of N,S-acetal formation, Knoevenagel reaction, aza-ene reaction, imine-enamine/keto-enol tautomerization, and N-cyclization as key steps. The merit of this protocol is highlighted by its easily available and economical starting materials, operational simplicity, efficient utilization of all the reactants, clean reaction profile, simple workup procedure, and tolerance of a wide variety of functional groups. © 2015 The Royal Society of Chemistry.
Chemoselective one-pot access to benzo[e]indole-4,5-diones and naphtho[2,1-b]thiophene-4,5-diones via copper-catalyzed oxidative [3 + 2] annulation of α-oxoketene N,S-acetals/β-ketothioamides with α-/β-naphthols
(Elsevier Ltd, 2018) Dhananjay Yadav; Gaurav Shukla; Monish A. Ansari; Abhijeet Srivastava; Maya Shankar Singh
An operationally simple and efficient one-pot method for the synthesis of 1-aroyl (or alkanoyl)-2-thioalkyl-3-aryl (or alkyl)-3H-benzo[e]indole-4,5-diones and naphtho[2,1-b]thiophene-4,5-diones has been devised by copper-catalyzed cross-coupling of α-oxoketene N,S-acetals/β-ketothioamides with α-/β-naphthols in open air for the first time. The key to the success of this transformation is the room temperature oxidation of α-/β-naphthol to 1,2-naphthoquinone as a reactive species, which undergoes formal [3 + 2] annulation with α-oxoketene N,S-acetals/β-ketothioamides via cascade sequence of Michael addition/tautomerization/oxidation/cyclization/aromatization reactions, enabling addition of a pyrrole/thiophene ring onto naphthoquinone moiety. Further, benzo[e]indole-4,5-diones were transformed to pentacyclic fused phenazine derivatives under solvent-free conditions. Based on our experimental outcomes, a tentative mechanistic rationale for this chemoselective protocol is proposed, which is well validated and supported by the control experiments. © 2018 Elsevier Ltd
Comparative study of squeezing-assisted Mach–Zehnder interferometer under homodyne, product detection and first-order correlation measurements
(Springer, 2025) Anand Kumar; Gaurav Shukla; Devendra Kumar Mishra
Precision measurement plays an important role in the field of quantum metrology. Choosing an appropriate measurement scheme improves measurement outcomes. Homodyne detection schemes, product detection schemes and correlation measurement schemes are the detection schemes that provide better information than the intensity detection schemes. Here, we compare the performance of all three detection schemes on a squeezing-assisted Mach–Zehnder interferometer in real scenarios. This comparison helps in the application of quantum sensing. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.
Copper(II)-Catalyzed [3+2] Annulation of Thioamides with AIBN: Facile Access to Highly Functionalized Thiazolidin-4-ones
(Georg Thieme Verlag, 2022) Pragya Pali; Dhananjay Yadav; Gaurav Shukla; Maya Shankar Singh
An efficient and versatile copper-catalyzed intermolecular radical [3+2] annulation of thioamides with azobisisobutyronitrile (AIBN) is described. This two-component copper(II)-catalyzed transformation is achieved in one pot via cascade formation of C-S/C-N bonds through cyclization of an in situ generated N,S-acetal intermediate derived from a?-ketothioamide. This operationally simple method allows direct access to synthetically demanding thiazolidin-4-ones in good to excellent yields containing diverse functional groups of different electronic and steric nature. The readily available reaction partners, the avoidance of expensive/toxic reagents and a gram-scale synthesis are additional attributes of this strategy. AIBN plays a dual role as a radical initiator and an unusual source of a two-carbon coupling partner. Notably, the products possess Z stereochemistry with regard to the exocyclic C=C double bond at position 2 of the thiazolidine ring. © 2021. Thieme. All rights reserved.
Copper-Catalyzed One-Pot Cross-Dehydrogenative Thienannulation: Chemoselective Access to Naphtho[2,1-b]thiophene-4,5-diones and Subsequent Transformation to Benzo[a]thieno[3,2-c]phenazines
(American Chemical Society, 2018) Gaurav Shukla; Abhijeet Srivastava; Dhananjay Yadav; Maya Shankar Singh
A facile, cost-effective, and highly efficient copper-catalyzed, TEMPO-mediated straightforward synthesis of 2,3-disubstituted naphtho[2,1-b]thiophene-4,5-diones has been achieved via cross-dehydrogenative thienannulation. The reaction proceeded via in situ generated naphthalene-1,2-diones by dearomatization of β-naphthols, followed by oxidative heteroannulation with α-enolic dithioesters chemoselectively in an open flask. Further, the naphtho[2,1-b]thiophene-4,5-diones undergo l-proline-catalyzed cross-dehydrative coupling with ortho-phenylenediamine enabling pentacyclic benzo[a]thieno[3,2-c]phenazines in good yields under solvent-free conditions. A mechanistic rationale for this cascade reaction sequence is well supported by the control experiments. © 2018 American Chemical Society.
DMAP mediated one-pot domino thienannulation: A versatile, regioselective and green mechanochemical route to naphtho[2,3-b]thiophenes
(2013) Gaurav Shukla; Girijesh Kumar Verma; Anugula Nagaraju; Rajiv Kumar Verma; Kesha Raghuvanshi; Maya Shankar Singh
Solvent-free mechanochemical route to naphtho[2,3-b]thiophenes via [3 + 2] oxidative heteroannulation of α-enolicdithioesters and β-oxothioamides with 1,4-naphthoquinone has been achieved at room temperature. © 2013 The Royal Society of Chemistry.
DMAP-promoted cascade CeS/CeN bonds formation approach to 1,3-thiazolidin-4-ones via annulation of β-ketothioamides with α-halocarboxylic acids at room temperature
(Elsevier Ltd, 2014) Girijesh Kumar Verma; Gaurav Shukla; Anugula Nagaraju; Abhijeet Srivastava; Maya Shankar Singh
An operationally simple and efficient one-pot straightforward method for the construction of 1,3-thiazolidin-4-ones has been developed by cyclocondensation of β-ketothioamides and an in situ generated acid anhydride from α-halocarboxylic acid in the presence of DCC at room temperature. The attractive features of this strategy include metal-free mild reaction conditions, short reaction time, and efficacy of forming consecutive CeS and CeN bonds and one ring in a single synthetic operation. Noteworthy, a Z-stereochemistry was observed for the exocyclic α-oxoketene moiety at 2-position of 1,3-thiazolidine ring. © 2014 Elsevier Ltd. All rights reserved.
DMAP-promoted domino annulation of β-ketothioamides with internal alkynes: A highly regioselective access to functionalized 1,3-thiazolidin-4-ones at room temperature
(2014) Girijesh Kumar Verma; Gaurav Shukla; Anugula Nagaraju; Abhijeet Srivastava; Keshav Raghuvanshi; Maya Shankar Singh
DMAP-mediated rapid and efficient one-pot regioselective access to functionalized 1,3-thiazolidin-4-ones via annulation of β-ketothioamides with internal alkynes has been achieved under mild reaction conditions. The merit of this straightforward domino protocol is highlighted by its operational simplicity, short reaction time, tolerance of a large variety of functional groups, and efficiency of producing two new bonds (C-S and C-N) and one thiazolidine ring. © The Royal Society of Chemistry 2014.
Easy access to α-hydroxyimino-β-oxodithioesters and application towards the synthesis of diverse 1,4-thiazine-3-ones via reduction/annulation cascade
(Elsevier Ltd, 2014) Anugula Nagaraju; Gaurav Shukla; Abhijeet Srivastava; B. Janaki Ramulu; Girijesh Kumar Verma; Keshav Raghuvanshi; Maya Shankar Singh
An operationally simple and facile synthesis of α-hydroxyimino- β-oxodithioesters has been achieved by nitrosation of α- enolicdithioesters. They were further treated with internal alkynes to afford diverse 1,4-thiazin-3-ones via domino reduction/annulation strategy under mild reaction conditions. Importantly, this is the first straightforward entry to highly functionalized 1,4-thiazin-3-one derivatives from simple starting materials. © 2014 Elsevier Ltd. All rights reserved.
Eco-efficient, regioselective and rapid access to 4,5-disubstituted 1,2,3-thiadiazoles via [3 + 2] cycloaddition of α-enolicdithioesters with tosyl azide under solvent-free conditions
(Royal Society of Chemistry, 2013) Maya Shankar Singh; Anugula Nagaraju; Girijesh Kumar Verma; Gaurav Shukla; Rajiv Kumar Verma; Abhijeet Srivastava; Keshav Raghuvanshi
An efficient, sustainable, and regioselective one-pot synthesis of hitherto unreported 4-aroyl/hetaroyl/alkanoyl-5-alkyl/allyl/benzylsulfanyl-1,2,3- thiadiazoles has been achieved by [3 + 2] cycloaddition of α- enolicdithioesters with tosyl azide through cascade 1-2 (S-N) and 3-4 (C-N) bond connections involving Wolff-type heterocyclization. Optimally, the reactions are very fast and completed within 2-15 minutes, when a mixture of α-enolicdithioester and tosyl azide was stirred at 0°C in the presence of Et3N under solvent-free conditions. Furthermore, no co-catalyst or activator is necessary. The eco-compatibility, mild conditions, excellent yields, easy purification, and avoidance of expensive/toxic reagents are advantages of this protocol to access this medicinally privileged substructure. © 2013 The Royal Society of Chemistry.
Electrochemical Hydroxylation of α-Bromoacetophenones: Access to α-Hydroxyacetophenones
(John Wiley and Sons Inc, 2024) Saurabh Singh; Subhasish Ray; Gaurav Shukla; Malkeet Singh; Maya Shankar Singh
Herein, a new method has been developed for the synthesis of various α-hydroxyacetophenones via an electro-oxidation process. It involves electrocatalytic hydroxylation via debromination of C(sp3)−Br bond. Here, simultaneous breaking of carbon-bromine (C−Br) bond and formation of a new carbon-oxygen (C−O) bond has been achieved through electrolysis of H2O using binary mixture of water and DMSO. The protocol features easy performance, oxidant and base-free mild conditions and short reaction time. © 2024 Wiley-VCH GmbH.