Govindasamy Sekar
@sekargroup.com
Professor, Department of Chemistry, IIT Madras, INDIA
IIT Madras
RESEARCH, TEACHING, or OTHER INTERESTS
Chemistry, Organic Chemistry
Scopus Publications
Scopus Publications
Solai Pandidurai, Venkata Surya Kumar Choutipalli, Venkatesan Subramanian, and Govindasamy Sekar
American Chemical Society (ACS)
An efficient approach for the synthesis of chiral pyrrolo[1,2-d][1,4]thiazine-2-carbaldehydes is achieved via formal 1,3-dipolar cycloaddition/rearrangement reactions of benzothiazolium salt and α,β-unsaturated aldehydes, utilizing an asymmetric organocatalyst. This process results in the formation of fluorescent, highly enantioenriched chiral molecules with three contiguous stereogenic centers, one of which is a chiral quaternary center, with excellent yields and enantio- and diastereoselectivity. A computational study demonstrated the understanding of the reaction mechanism. The synthetic utility of this protocol was successfully employed for gram scale synthesis. Fluorescent and in silico studies showed the application of the present methodology.
Govindasamy Sekar, Vysakh Venugopalan Nair, and Jieping Zhu
Royal Society of Chemistry (RSC)
This tutorial review will focus on the recently evolved chalcogen bonding catalysis. Emphasis will be given to the basics of non-covalent bonding, chiral chalcogen bonding catalysis, chiral separation, and chalcogen bonding in biomolecules.
Gollapalli Narasimha Rao and Govindasamy Sekar
American Chemical Society (ACS)
An efficient, commercially available, and reusable copper-oxide nanoparticle (CuO-NPs) and (R)-(-)-DTBM SEGPHOS catalyzed chemo- and enantioselective reduction of α-keto amides to α-hydroxy amides has been developed. The scope of the reaction has been studied with various α-keto amides containing electron-donating and electron-withdrawing groups affording the enantiomerically enriched α-hydroxy amides in good yields with excellent enantioselectivity. The CuO-NPs catalyst has been recovered and reused up to four catalytic cycles without any significant change in particle size, reactivity, and enantioselectivity.
Naziya Parveen, Solai Pandidurai, and Govindasamy Sekar
American Chemical Society (ACS)
Stereoselective, one-pot synthesis of 3-arylidene-2-oxindoles has been accomplished via Heck-like carbocyclization/nucleophilic addition of N-(2-iodophenyl)-N-methyl-3-phenylpropiolamide, phenylacetylene, and secondary amine using binaphthyl stabilized palladium nanoparticles (Pd-BNP) as a reusable catalyst. Less reactive aryl bromides generally provided a similar yield of 3-arylidene-2-oxindoles compared with more reactive aryl iodides. The Pd-BNP nanocatalyst has been recovered and recycled for five catalytic cycles with only an insignificant reduction in particle size, reactivity, and reaction yield.
Gollapalli Narasimha Rao and Govindasamy Sekar
Royal Society of Chemistry (RSC)
A Pd-nanoparticle catalyzed synthesis of symmetrical 1,2-dicarbonyl compounds was developed from alkynes, which was further extended to the synthesis of unsymmetrical 1,2-dicarbonyl compounds.
Leena Gautam, R. Sarathi, P. Soundarya, G. Sekar, U. Mohan Rao, and I. Fofana
Institute of Electrical and Electronics Engineers (IEEE)
Anuradha Nandy and Govindasamy Sekar
Wiley
AbstractThe efficiency of dibenziodolium salts as halogen bond donor catalysts was investigated by studying various organic transformations. Diverse reactions were carried out with low catalytic loading and under mild conditions. The catalyst was found to be efficient for carrying out the reduction of quinolines, one‐pot reductive amination, Michael addition reaction of indoles with chalcones, and Friedel‐Crafts reaction of indoles with isatin with a low catalytic loading of 3 mol %. A wide substrate scope was attempted for all the transformations. Several control experiments were carried to rule out the possibility of hidden Brønsted acid catalysis. NMR studies and preliminary DFT calculations suggest the presence of halogen bond between the catalyst and the substrate.
Imran Kazi, Anuradha Nandy, Raji Selvam, and Govindasamy Sekar
American Chemical Society (ACS)
An efficient method for transition metal-free halogen bond-assisted regioselective C-H arylation of 2-phenylimidazo-[1,2-a]pyridines under visible-light condition has been developed. The halogen bond between an aryl halide and base KOtBu initiates an electron transfer process and generates an aryl radical, which catalyzes its coupling with 2-phenylimidazo-[1,2-a]pyridines to give arylated products in good yield. Several control experiments, density functional theory calculations, and ultraviolet-visible analysis indicate the presence of a halogen bond between an aryl halide and KOtBu. This methodology has been successfully utilized to synthesize antileishmanial agents.
Palanisamy Soundarya and Govindasamy Sekar
Royal Society of Chemistry (RSC)
An efficient method for synthesizing thioaurones has been developed using xanthate as sulfur surrogate. This reaction's key success lies in the use of iodine as a reagent, which promotes the α-iodination followed by cyclization of saturated ketones.
Vysakh Venugopalan Nair, Dhanarajan Arunprasath, Solai Pandidurai, and Govindasamy Sekar
Wiley
AbstractDual Catalysis has enabled a plethora of novel unconventional transformations that would have been unattainable by either catalyst alone. The enormous potential of dual catalysis hinges on the synergistic activation of two substrates in discrete catalytic cycles without interfering with one another. The last decade had witnessed diverse dual‐catalyst systems focusing mainly on the combination of transition metal catalysis with either one of Lewis acid catalysis, photoredox catalysis, biocatalysis or organocatalysis (i. e., Lewis bases, Brønsted acids and NHC catalysts). In this setting, the scientific community has greatly embraced the integration of amine catalysts with transition metal catalysts. This Review comprehends the reported examples from the past decade on dual amine/transition metal catalysis and discuss the various activation modes for the functionalisation of carbonyl compounds.
Anuradha Nandy and Govindasamy Sekar
American Chemical Society (ACS)
An iodine-catalyzed denitrative C-S cross-coupling reaction has been developed to attain thiochromanones from 2'-nitrochalcones and xanthate. The strategy was extended for a three-component synthesis of thiochromenes via intermolecular C-S cross-coupling followed by aldol reaction. The reaction proceeds via activation of the keto group of chalcone through a halogen bond complex with iodine/denitrative C-S bond formation with xanthate/sulfa-Michael addition to chalcones. The methodology was also demonstrated for chemoselective reduction of chalcones. The protocol was also employed to synthesize biologically important 3'-hydroxythioflavone and thiochromenones.
Somraj Guha, Imran Kazi, Dhamodharan Sathish, and Govindasamy Sekar
American Chemical Society (ACS)
The development of direct and controlled oxidation of C(sp3)-H bonds is of great importance. Herein, an iodine-catalyzed controlled oxidation of (aryl)(heteroaryl)methanes to (aryl)(heteroaryl)methanols is disclosed under metal-free reaction conditions. A catalytic system comprised of iodine/silyl chloride with HI as an additive in the presence of dimethyl sulfoxide selectively oxidizes the C(sp3)-H bonds without being overoxidized to corresponding ketones. Therapeutically important aryl heteroaryl methanol derivatives were obtained in good yields. The preliminary mechanistic investigation proves that the primary source of oxygen is DMSO.
Anuradha Nandy and Govindasamy Sekar
American Chemical Society (ACS)
An efficacious and mild KOtBu-promoted intramolecular C-S cross-coupling of ortho-iodothioanilides in conjunction with a catalytic quantity of phenanthroline as an additive has been described for the convenient synthesis of 2-substituted benzothiazoles. The methodology is suitable for attaining a wide variety of 2-alkyl- and 2-aryl-substituted benzothiazoles. Single-crystal XRD, DFT calculations, NMR, and UV studies suggest that halogen bonds between the units of ortho-iodothioanilides may assist in the electron transfer process.
Nallappan Sundaravelu, Tushar Singha, Anuradha Nandy, and Govindasamy Sekar
Royal Society of Chemistry (RSC)
Cu-catalyzed domino synthesis of multi-substituted benzo[b]thiophene via radical cyclization of 2-iodophenyl ketones has been developed using xanthate as a sulfur surrogate. Furthermore, it was extended for the synthesis of Lupinalbin analogues.
Nallappan Sundaravelu, Anuradha Nandy, and Govindasamy Sekar
American Chemical Society (ACS)
An efficient visible light mediated photocatalyst free C-S cross-coupling reaction has been developed for the synthesis of thiochromane derivatives through photoinduced electron transfer (PET). This methodology was further utilized for the synthesis of thiochroman-4-ol through intermolecular three-component cross-coupling reaction. The reaction proceeds via C-S bond formation through EDA complex/thioester cleavage/inter-or intramolecular sulfa-Michael addition followed by aldol reaction sequence. The EDA complex formation between aryl iodides and xanthate has been substantiated using spectroscopic experiments and DFT calculations.
Nallappan Sundaravelu, Subramani Sangeetha, and Govindasamy Sekar
Royal Society of Chemistry (RSC)
This review presents the metal-catalyzed C–S bond-formation reaction to access organosulfur compounds using various sulfur surrogates with an extended discussion on the reaction mechanism, regioselectivity of product and pharmaceutical application.
Anuradha Nandy, Imran Kazi, Somraj Guha, and Govindasamy Sekar
American Chemical Society (ACS)
An efficient protocol for the synthesis of thioether directly from heteroarenes has been developed in the presence of visible light in a one-pot manner at room temperature. This method involves two sequential reactions in a single pot where the formation of the iodinated heteroarene is followed by a transition-metal-free C-S coupling reaction. A wide range of heteroarene and thiol partners (including aliphatic thiols) have been used for the synthesis of thioethers. NMR studies and DFT calculations revealed the presence of a halogen bond between the thiolate anion (halogen bond acceptor) and iodoheteroarene (halogen bond donor). This halogen bonded complex on photoexcitation facilitates the electron transfer from the thiolate anion to the iodoheteroarene at room temperature.
Subramani Sangeetha and Govindasamy Sekar
Royal Society of Chemistry (RSC)
Efficient domino methods are developed for the synthesis of 2,3-dihydrobenzo[b]thiophenes and 2-acylbenzo[b]thiophenes from 2-iodoketones using in situ generated iodine from by-product KI with a Cu-catalyst and xanthate.
Naziya Parveen and Govindasamy Sekar
American Chemical Society (ACS)
The binaphthyl stabilized palladium nanoparticles (Pd-BNP) catalyzed single-step, stereoselective domino synthesis of symmetrically and unsymmetrically all-carbon tetrasubstituted olefin containing oxindoles from readily accessible anilides has been developed. The Pd-BNP catalyst showed a wide range of functional group tolerance that enabled building a library of heteroaromatics. This reusable Pd catalyst reflected its utility in the synthesis of biologically important AMP-activated protein kinase deprived of any metal Pd contamination. The nanocatalyst was easily recovered and reused five times without any appreciable loss in particle size or catalytic activity.
Nallappan Sundaravelu and Govindasamy Sekar
Royal Society of Chemistry (RSC)
A copper catalyzed three-component synthesis of π-conjugated tetracyclic thiochromeno-quinolinone and thiochromeno-thioflavone was established via oxidative double hetero Michael addition using in situ generated nucleophiles.
Nallappan Sundaravelu, Somraj Guha, and Govindasamy Sekar
American Chemical Society (ACS)
The application of stabilized iodonium ions in organic synthesis remains largely unexplored. Herein, a metal free domino synthesis of Z-selective α,β-diphenylthio enones is developed from easily available benzylic secondary alcohols employing thiophenol stabilized iodonium ion as catalyst. This methodology was further extended to 5-membered and 6-membered cyclic secondary alcohols. The UV-Vis experiments suggest the formation of thiol-coordinated iodine (I) intermediates. Several control experiments establish that the reaction proceeds via the oxidation of alcohol to ketone, α-thiolation of ketones followed by α,β-unsaturation and finally the β-thiolation of α,β-unsaturated ketones to generate bis-vinyl sulfides. The in-situ generated stabilized iodonium ion is highly efficient to catalyze multiple functional group transformations in a in a domino manner.
Naziya Parveen and Govindasamy Sekar
American Chemical Society (ACS)
A single-step, stereoselective protocol for the synthesis of unsymmetrically substituted (E)-3-allylideneoxindole and (E)-3-allylidenebenzofuran from readily accessible starting materials using palladium binaphthyl nanoparticles (Pd-BNP) has been developed. Pd-BNP adept a wide range of functional group tolerance and an immense array of substrate scope have been explored with the successful synthesis of drug molecule "tubulin polymerization inhibitor" free from trace metal impurities. The model reaction is extended to a gram-scale synthesis and one of the product is utilized for derivatization. The Pd-BNP has been recycled up to 5 catalytic cycles without any loss in reaction yields and particle size of nanoparticles.
Naziya Parveen and Govindasamy Sekar
Wiley
AbstractAn efficient protocol for the straightforward, single‐step synthesis of 3‐aryl‐1‐indanones from 2′‐iodochalcone via reductive Heck reaction using phosphine free, stable and reusable binaphthyl stabilized palladium nanoparticle (Pd‐BNP) as a catalyst has been described. An immense array of substrate scope with electron‐rich and deficient 2′‐iodochalcones have been synthesized. Further derivatization of product indanones have been achieved successfully. The heterogeneous nature of the Pd‐BNP has been validated by centrifugation test and mercury poisoning experiment. Pd‐BNP has been successfully recycled up to 5 cycles without any significant loss in reaction yield and particle size of nanoparticles, confirmed by TEM analysis.magnified image
Naziya Parveen, Alagesan Muthukumar, and Govindasamy Sekar
Wiley
AbstractA mild, efficient, and stable binaphthyl‐stabilized palladium nanoparticles (Pd−BNP) catalyzed (sp3)C−H reaction of 2‐alkylazaarenes with activated carbonyl compounds was developed. Various activated carbonyl compounds such as α‐keto amide, isatin, 1,2‐diketone, α‐keto ester, trifluoromethyl ketone, and phenylglyoxal derivatives were examined and most of the compounds underwent the reaction smoothly to provide the corresponding products in moderate to excellent yields. Moreover, chemoselective reactions of α‐keto amides in the presence of simple ketones were achieved. Also, the model reaction was extended to a gram‐scale synthesis and some of the products were utilized for derivatization to form the corresponding N‐oxides, acryl amides and 1,2‐diol, respectively. The major advantages of the protocol are neutral reaction conditions, no additional requirement of external ligand, and successful reusability of the Pd−BNP catalyst up to five cycles without losing its activity and yield. Hg‐poisoning and hot filtration tests confirmed the heterogeneity of the Pd−BNP catalyst.magnified image