Sekar Research Group

Department of Chemistry • IIT Madras • INDIA

From IIT Madras

  1. An Efficient, Mild and Intermolecular Ullmann-Type Synthesis of Thioethers Catalyzed by Diol-Copper(I)Complex
    (D.J.C. Prasad, and G. Sekar, Synthesis, 2009, In Press)
    2. A wide range of diaryl thioethers and aryl alkyl thioethers are synthesized under mild reaction conditions from the corresponding aryl iodides and aromatic/aliphatic thiols through Ullmann type intermolecular coupling reactions in the presence of catalytic amount of easily available novel DIOL-CuBr complex at 82 oC. The catalytic system is not only capable of coupling electron-withdrawing and electron-releasing substituent containing substrates but also tolerates a broad range of functional groups including heteroatom containing aryl iodides and thiols.

  2. Copper(I)-Catalyzed Caryl¡VCalkynyl Bond Formation of Aryl Iodides with Terminal Alkynes
    (K. G. Thakur, G. Sekar, Synthesis, 2009, 2785)
    3. A wide range of internal alkynes are synthesized from the corresponding aryl iodides and terminal alkynes by Sonogashira type cross-coupling reactions through C(aryl)-C(alkynyl) bond formation in the presence of a catalytic amount of easily available DBU-CuBr complex under mild reaction conditions.

  3. Highly efficient copper catalyzed domino ring opening and Goldburg coupling cyclization for the synthesis of 3, 4-dihydro-2H-1,4-benzoxazines
    (R. K. Rao, A. B. Naidu, and G. Sekar, Org Lett., 2009, 11, 1923)
    One of the most accessed top 20 papers in Organic Letters for the month of April 2009
    4. trans-3,4-Dihydro-2H-1,4-benzoxazine moieties can be synthesized by domino aziridine ring opening with o-iodophenols followed by the copper catalyzed Goldberg coupling cyclization (intramolecular C(aryl)-N(amide) bond formation) with good to excellent yields.

  4. Chiral cobalt catalyzed enantiomer-differentiating oxidation of racemic benzoins using molecular oxygen as stoichiometric oxidant
    (S. K.Alamsetti, P. Muthupandi and G. Sekar, Chem. Eur. J., 2009, 15, 5424)
    5. An efficient enantioselective oxidative reaction catalyzed by chiral cobalt complex has been developed using molecular oxygen as the stoichiometric oxidant. The very mild reaction conditions of the catalytic system provide access to a wide range of benzoins (Ą-hydroxy ketones) in high yield and excellent enantioselectivity (s (kf / ks) up to 47). This method is very versatile in that the sole by-product accompanying our oxidation process is water making our system more eco-friendly and green as well.

  5. Chiral iron complex catalyzed enantioselective oxidation of racemic benzoins
    (P. Muthupandi, S. K.Alamsetti and G. Sekar, Chem. Commun., 2009, 3288)
    6. An efficient, economic and environmental friendly enantioselective oxidation of racemic benzoins (Ą-hydroxy ketones) catalyzed by chiral iron complex has been developed using molecular oxygen as a terminal oxidant with good selectivity and excellent enantiomeric excess.

  6. An efficient copper(I) complex catalyzed Sonogashira type cross-coupling of aryl halides with terminal alkynes
    (K. G. Thakur, E. A. Jaseer, A. B. Naidu and G. Sekar, Tetrahedron Lett., 2009, 50, 2965)
    7. A wide range of arylated alkynes are synthesized from the corresponding aryl halides and terminal alkynes by Sonogashira type cross-coupling reactions through C(aryl)-C bond formation in the presence of a catalytic amount of N,N¡¦-dibenzyl BINAM-CuI complex under mild reaction conditions.

  7. An efficient, mild and selective Ullmann-type N-arylation of indoles catalyzed by copper(I) complex
    (R. K. Rao, A. B. Naidu, E. A. Jaseer and G. Sekar, Tetrahedron , 2009, 65, 4619)
    8. A wide range of N-arylated indoles are selectively synthesized through intermolecular C(aryl)-N bond formation from the corresponding aryl iodides and indoles through Ullmann type coupling reactions in the presence of a catalytic amount of easily available N,N,N¡¦,N¡¦-tetramethyl BINAM-CuI complex under very mild reaction conditions.

  8. A general, mild and intermolecular Ullmann-type synthesis of diaryl and alkyl aryl ethers catalyzed by diol-copper(I) complex
    (A. B. Naidu, E. A. Jaseer and G. Sekar, J. Org. Chem, 2009, 74, 3675)
    One of the most accessed top 10 papers in Journal of Organic Chemistry for the month of April-June 2009
    9. A wide range of diaryl ethers and alkyl aryl ethers are synthesized through intermolecular C(aryl)-O bond formation from the corresponding aryl iodides/aryl bromides and phenols/alcohols through Ullmann type coupling reaction in the presence of a catalytic amount of easily available (¡Ó)-diol L3-CuI complex under very mild reaction conditions. Less reactive aryl bromides can also used for O-arylation of phenols under the same reaction conditions without increasing the reaction temperature, catalyst loading and time. The catalytic system is not only capable of coupling hindered substrate but also tolerates a broad range of a series of functional groups.

  9. An enantiopure galactose oxidase model: synthesis of chiral amino alcohols through oxidative kinetic resolution catalyzed by chiral copper complex
    (S. Mannam, and G. Sekar, Tetrahedron: Asymmetry, 2009, 20, 495)
    10. An enantiopure Galactose Oxidase (GO) enzyme¡¦s model has been synthesized from readily available (R)-BINAM and Cu(OTf)2 and the enantiopure GO model has been effectively used in situ as an efficient chiral catalyst for the synthesis of chiral amino alcohols through oxidative kinetic resolution (OKR) where molecular oxygen is used as sole oxidant. Under the proposed catalytic conditions both ortho- and para-substituted amino alcohols resolved with good to excellent enantiomeric excesses through oxidative kinetic resolution.

  10. An efficient intermolecular C(aryl)-S bond forming reaction catalyzed by BINAM-copper(II) complex
    (D.J.C. Prasada, Ajay B. Naidu and G. Sekar, Tetrahedron Lett.,2009,50, 1411)
    11. A wide range of diaryl thioethers and aryl alkyl thioethers are synthesized from the corresponding aryl iodides and aromatic/aliphatic thiols through Ullmann type intermolecular coupling reactions in the presence of a catalytic amount of easily available BINAM-Cu(OTf)2 complex. Less reactive aryl bromides have also been shown to react with thiols under identical reaction conditions to give good yields of the thioethers without increasing the reaction temperature and time.

  11. Galactose Oxidase Model: Biomimetic, Enantiomer-Differentiating Oxidation of Alcohols by Chiral Copper Complex
    (Santosh Kumar Alamsetti, Sreedevi Mannam, P. Muthupandi, G. Sekar, Chem. Eur. J.,2008, 15, 1086)
    12. An enantiopure Galactose Oxidase enzyme?s model has been synthesized from readily available (R)-BINAM & Cu(OTf)2 and this enantiopure GO model has been effectively used as an efficient chiral catalyst for oxidative kinetic resolution of secondary alcohols.This is the first chiral copper catalyzed oxidative kinetic resolution of racemic benzoins and the simplest method for the synthesis of highly important enantiomerically enriched benzoins.

  12. An efficient intermolecular BINAM-copper (I) catalyzed Ullmann coupling of aryl iodides/bromides with aliphatic alcohols
    (Ajay B. Naidu and G. Sekar,Tetrahedron Lett.,2008, 49, 3147)
    13. A wide range of alkyl aryl ethers are synthesized from the corresponding aryl iodides and aliphatic alcohols through Ullmann type intermolecular coupling reactions in the presence of a catalytic amount of easily available BINAM-CuI complex. Less reactive aryl bromides have also been shown to react with aliphatic alcohols under identical reaction conditions to give good yields of the alkyl aryl ethers without increasing the reaction temperature and time

  13. CuCl catalyzed selective oxidation of primary alcohols to carboxylic acids with tert-butyl hydroperoxide at room temperature
    (Sreedevi Mannam and G. Sekar,Tetrahedron Lett.,2008, 49, 2457)
    14. Direct oxidation of primary alcohols to the corresponding carboxylic acids is performed highly efficiently at room temperature with anhydrous tert-butyl hydroperoxide in the presence of a catalytic amount of CuCl under ligand free conditions in acetonitrile. Benzylic alcohols and allylic alcohols are more reactive than aliphatic alcohols and are selectively oxidized to the corresponding acids in the presence of aliphatic alcohols such as 1-octanol and 1-decanol.

  14.  CuCl catalyzed oxidation of aldehydes to carboxylic acids with aqueous tert-butyl hydroperoxide under mild conditions
    (Sreedevi Mannam and G. Sekar,Tetrahedron Lett.,2008, 49, 1083)
    15. Oxidation of aldehydes to corresponding carboxylic acids can be performed highly efficiently at room temperature with 70% tert-butyl hydroperoxide (in water) in the presence of catalytic amount of easily available ligand free CuCl in acetonitrile solvent under very mild conditions. The new oxidation protocol works well for all kinds of aldehydes including aliphatic aldehydes and aliphatic dialdehydes.

  15.  An efficient BINAM-Copper(II) catalyzed Ullmann-type synthesis of diaryl ethers
    (Ajay B. Naidu, O. R. Raghunath, D. J. C. Prasad and G. Sekar,,Tetrahedron Lett.,2008,49,1057)
    16. A wide range of diaryl ethers are synthesized from the corresponding aryl iodides and phenols through Ullmann type coupling reactions in the presence of a catalytic amount of easily available BINAM-Cu(OTf)2 complex under mild reaction conditions. Less reactive aryl bromides have also been shown to react with phenols under identical reaction conditions to give good yields of the diaryl ethers without increasing the reaction temperature and time.

  16.  Aerobic, Chemoselective Oxidation of Alcohols to Carbonyl Compounds Catalyzed by DABCO-Copper Complex under Mild Conditions
    (S. Mannam, S. K. Alamsetti and G. Sekar, Adv. Synth. Catal., 2007, 349, 2253)
    17. DABCO-CuCl complex (5 mol %) along with TEMPO (5 mol%) in nitromethane solvent used as an efficient catalytic system for the selective oxidation of benzylic and allylic alcohols into corresponding carbonyl compounds at room temperature where molecular oxygen acts as an ultimate, stoichiometric oxidant and water is the only by-product. Solid state structure determination of DABCO-Copper complex shows that the copper is in copper(II) oxidation state with trigonal bipyramidal geometry and exists in linear polymeric structure due to strong hydrogen bonding

  17.  Highly stereoselective chlorination of -substituted cyclic alcohols using PPh3?NCS: factors that control the stereoselectivity
    (E. A. Jaseer, Ajay B. Naidu, Sreehari S. Kumar, R. Koteshwar Rao, Krishna G. Thakur and G. Sekar, Chem. Commun., 2007, 867)
    18. A variety of trans--substituted cyclic alcohols were stereoselectively chlorinated to either the corresponding cis-chloride or trans-chloride (inversion or retention of configuration) with good to excellent yields; the stereochemical outcome is determined by the size of the ring and the nature of the -substituents, especially the electronegativity of the substituted atom.
From Ph.D and postdoctoral work
  1.  Catalyzed-Controlled Stereoselective Combinatorial Synthesis.
    (L. F. Tietze, N. Rackelmann and G. Sekar Angew. Chem. Int. Ed. 2003, 42, 4254)
  2.  Non-enzymatic Kinetic Resolution of b-amino Alcohols: Chiral BINAP Mediated SN2 Displacement of Hydroxy Groups by Halogens through Formation of an Aziridinium Ion Intermediate.
    (G. Sekar and H. Nishiyama Chem. Commun. 2001, 1314)
  3.  Nonenzymatic Kinetic Resolution of Secondary Alcohols: Enantioselective SN2 Displacement of Hydroxy Groups by Halogens in the Presence of Chiral BINAP.
    (G. Sekar and H. Nishiyama J. Am. Chem. Soc. 2001, 123, 3603)
  4.  An Efficient method for Opening of Nonactivated Aziridines with TMS Azide: Application in the Synthesis of Chiral 1, 2- Diaminocyclohexane.
    (M. Chandrasekhar, G. Sekar and V. K. Singh Tetrahedron Lett. 2000, 41, 10079)
  5.  An Efficient Method for the Cleavage of Aziridines with Hydroxyl Compounds.
    (B. A. Bhanu Prasad, G. Sekar and V. K. Singh Tetrahedron Lett. 2000, 41, 4677)
  6.  Enantiomerically Pure N-aryl-β-Amino Alcohols by Enzymatic Resolution.
    (G. Sekar R. M. Kamble and V. K. Singh Tetrahedron: Asymmetry, 1999, 10, 3663).
  7.  Efficient Method for Cleavage of Aziridines with Aromatic Amines.
    (G. Sekar and V. K. Singh, J. Org. Chem., 1999, 64, 2537).
  8.  An Efficient Method for Cleavage of Epoxides with Aromatic Amines.
    (G. Sekar and V. K. Singh, J. Org. Chem., 1999, 64, 287).
  9.  Asymmetric Kharasch Reaction: Allylic Oxidation of Olefins Using Chiral Pyridine Bis (diphenyoxazoline)-Copper Complexes and tert-Butyl perbenzoate.
    (G. Sekar, A. DattaGupta and V. K. Singh, J. Org. Chem., 1998, 63, 2961).
  10.  Catalytic Enantioselective Cyclopropanation of Olefins Using Carbenoid Chemistry.
    (V. K. Singh, A. DattaGupta and G. Sekar, Synthesis, 1997, 137).
  11.  Cu (OTf)2-DBN/DBU Complex as an Efficient Catalyst for Allylic Oxidation of Olefins With tert-Butyl perbenzoate.
    (G. Sekar, A. DattaGupta and V. K. Singh, Tetrahedron Lett. 1996, 37, 8435).

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