Browsing by Author "Girijesh Kumar Verma"

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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.
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.
Construction of five- and six-membered heterocycles on both Cp rings of the ferrocene moiety of α-oxoketene-S,S-acetal and β-oxodithioester via heteroaromatic annulation
(Royal Society of Chemistry, 2013) Girijesh Kumar Verma; Rajiv Kumar Verma; Maya Shankar Singh
1,1′-Bis(1,1-dimethylsulfanyl-3-oxo-1-propene)ferrocene and 1,1′-Bis(methyl-3-hydroxy-prop-2-ene-dithioate)ferrocene have been shown to be useful three-carbon synthons for the efficient synthesis of hitherto unreported and synthetically demanding Fc-heterocycles. Five-membered (pyrazole, isoxazole, and thiophene) and six-membered (pyrimidine, coumarin, and quinoline) heterocycles have been constructed on both Cp rings of the ferrocene matrix via regioselective heteroaromatic annulation. © The Royal Society of Chemistry.
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.
In(OTf)3-catalysed one-pot versatile pyrrole synthesis through domino annulation of α-oxoketene-N,S-acetals with nitroolefins
(Royal Society of Chemistry, 2014) Abhijeet Srivastava; Gaurav Shukla; Anugula Nagaraju; Girijesh Kumar Verma; Keshav Raghuvanshi; Raymond C. F. Jones; Maya Shankar Singh
In(OTf)3-catalyzed robust and sustainable one-pot access to previously unknown and synthetically demanding polysubstituted pyrroles via [3 + 2] annulation of α-oxoketene-N,S-acetals with β-nitrostyrenes has been achieved under solvent-free conditions. The merit of this domino Michael addition/cyclization sequence is highlighted by its operational simplicity, short reaction time (5-10 min), good to excellent yields, tolerance of a large variety of functional groups, and efficiency of producing two new (C-C and C-N) bonds and one highly functionalized pyrrole ring in a single operation, which make it an ideal alternative to existing methods. This journal is © the Partner Organisations 2014.
In(OTf)3-mediated dehydrative annulation of β-ketothioamides with phenylglyoxal: One-pot access to diversely functionalized pyrrol-2-thiones
(Elsevier Ltd, 2014) Girijesh Kumar Verma; Gaurav Shukla; Anugula Nagaraju; Abhijeet Srivastava; Maya Shankar Singh
Indium triflate mediated first synthesis of diversely functionalized pyrrol-2-thiones has been developed by dehydrative annulation of β-ketothioamides with phenylglyoxal through the domino Knoevenagel condensation/cyclization cascade in one-pot. This new simple strategy not only utilizes readily accessible starting material, but also allows the construction of 5-membered azaheterocycle with one quaternary carbon center as a result of the formation of two new (C-C and C-N) bonds in a single operation. © 2014 Elsevier Ltd. All rights reserved.
InCl 3 catalyzed domino route to 2H-chromene-2-ones via [4 + 2] annulation of 2-hydroxyarylaldehydes with α-oxoketene dithioacetal under solvent-free conditions
(2012) Rajiv Kumar Verma; Girijesh Kumar Verma; Gaurav Shukla; Maya Shankar Singh
A facile and efficient synthesis of 3-aroyl/heteroaroyl/ferrocenoyl/ alkanoyl-2H-chromen-2-ones has been developed by the cyclocondensation of α-oxoketene dithioacetals and 2-hydroxyarylaldehydes catalyzed by InCl 3 under solvent-free conditions. No co-catalyst or activator is needed and MeSH is the only by-product of this protocol. The methodology involves ring annulation of 2-hydroxyarylaldehydes with a variety of α-oxoketene dithioacetals offering rapid entry into differentially substituted chromen-2-ones. The condensation of ferrocene derived α-oxoketene dithioacetal and 2-hydroxyarylaldehyde furnished coumarin installed on a ferrocene platform. © 2012 The Royal Society of Chemistry.
Molecular docking and in vitro antileishmanial evaluation of chromene-2-thione analogues
(2012) Rajiv Kumar Verma; Vijay Kumar Prajapati; Girijesh Kumar Verma; Deblina Chakraborty; Shyam Sundar; Madhukar Rai; Vikash Kumar Dubey; Maya Shankar Singh
Leishmaniases are an epidemic in various countries, and the parasite is developing resistance against available drugs. Thus, development of new drugs against Leishmania is an open area of investigation for synthetic organic chemists. To meet this challenge, a series of chromene-2-thione derivatives have been synthesized and docked into the active site of trypanothione reductase (TryR) enzyme required for redox balance of the parasite. These were screened on promastigote, axenic amastigote, and intracellular amastigote stages of Leishmania donovani and found to show high levels of antileishmanial activity together with minimal toxicity to human peripheral blood mononuclear cells. Compounds 3b and 3k were found to be the most active among the tested compounds. Although the compounds show moderate antileishmanial activity, they identify a chemical space to design and develop drugs based on these chromene-2-thione derivatives against the Leishmania parasite. © 2012 American Chemical Society.
One-pot straightforward approach to 2,3-disubstituted benzo/naphtho[b] furans via domino annulation of α-oxoketene dithioacetals and 1,4-benzo/naphthoquinone mediated by AlCl3 at room temperature
(2013) Girijesh Kumar Verma; Rajiv Kumar Verma; Gaurav Shukla; Nagaraju Anugula; Abhijeet Srivastava; Maya Shankar Singh
A versatile and convenient one-pot direct approach to 2,3-disubstituted benzo/naphtho[b]furans via domino annulation of α-oxoketene dithioacetals and 1,4-benzo/naphthoquinone has been achieved in the presence of aluminium chloride at room temperature. This protocol represents an extremely simple, straightforward and rapid entry to highly substituted benzo/naphtho[b]furans in good yields from easily viable starting materials under mild reaction conditions. © 2013 Elsevier Ltd. All rights reserved.
Regioselectivity in the ring opening of epoxides: A metal-free cascade C-S/C-O bond formation approach to 1,3-oxathiolan-2-ylidenes through heteroannulation of α-enolic dithioesters at room temperature
(Georg Thieme Verlag, 2014) Gaurav Shukla; Anugula Nagaraju; Abhijeet Srivastava; Girijesh Kumar Verma; Keshav Raghuvanshi; Maya Shankar Singh
An operationally simple and efficient approach to hitherto unreported and synthetically demanding 1,3-oxathiolan-2-ylidenes has been developed. The approach involves a cascade [2+3] heteroannulation of α-enolic dithioesters with epoxides promoted by non-nucleophilic moderate base Cs 2CO3 at room temperature. Typical features of this strategy include metal-free mild reaction conditions, atom-economy, high yields, and efficacy of forming two consecutive C-S and C-O bonds, and one ring in a single stroke. MeSH is the only by-product, and the stereochemistry of the exocyclic α-oxoketene moiety of 1,3-oxathiolane was assigned to have Z-configuration. © Georg Thieme Verlag Stuttgart New York.
Solvent-free one-pot efficient and highly regioselective access to functionalized thiazolopyridones from α-enolic dithioesters
(Arkat, 2015) Anugula Nagaraju; B. Janaki Ramulu; Gaurav Shukla; Abhijeet Srivastava; Girijesh Kumar Verma; Maya Shankar Singh
An operationally simple, highly convergent and straightforward synthesis of diverse thiazolopyridones has been achieved via three-component domino coupling (3CDC) of α-enolic dithioesters, cysteamine and dialkyl acetylenedicarboxylates under solvent-free conditions. The approach is carbon-economic and relies on sequential cyclic N,S-acetal formation/Michael addition/N-cyclization cascade forming consecutive C-C, C-N and C-S bonds in one-pot. © ARKAT-USA, Inc.
β-Oxodithioesters
(2013) Girijesh Kumar Verma
(A) Samuel et al.4 reported the synthesis of thiophenes by alkylation of β-oxodithioester with α-haloketones. Depending on the combination of base and solvent, differently substituted thiophenes are obtained. (Chemical Equation) (B) β-Oxodithioester in the presence of DMAP reacted with dialkyl acetylenedicarboxylate to give 2,3,4-trisubstituted thiophenes in high yield in short reaction times. (Chemical Equation) (C) Samuel et al.6 have reported the synthesis of 2-ylidene-1,3-oxathioles in good yield using β-oxodithioester and α-haloketone in the presence of NaH in toluene. (Chemical Equation) (D) Chromene and benzochromene-2-thiones were efficiently synthesized in high yield by the reaction of β-oxodithioester and 2-hydroxy benzaldehyde/naphthaldehyde under solvent-free conditions using SiO2·H2SO4 as the catalyst. (Chemical Equation) (A) Samuel et al.4 reported the synthesis of thiophenes by alkylation of β-oxodithioester with α-haloketones. Depending on the combination of base and solvent, differently substituted thiophenes are obtained. (Chemical Equation) (B) β-Oxodithioester in the presence of DMAP reacted with dialkyl acetylenedicarboxylate to give 2,3,4-trisubstituted thiophenes in high yield in short reaction times. (Chemical Equation) (C) Samuel et al.6 have reported the synthesis of 2-ylidene-1,3-oxathioles in good yield using β-oxodithioester and α-haloketone in the presence of NaH in toluene. (Chemical Equation) (D) Chromene and benzochromene-2-thiones were efficiently synthesized in high yield by the reaction of β-oxodithioester and 2-hydroxy benzaldehyde/naphthaldehyde under solvent-free conditions using SiO 2·H2SO4 as the catalyst. (Chemical Equation). © Georg Thieme Verlag Stuttgart · New York.