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2017

  • 61. Palladium-Catalyzed C–H Activation: Mass Spectrometric Approach to Reaction Kinetics in Solution

    Palladium-Catalyzed C–H Activation: Mass Spectrometric Approach to Reaction Kinetics in Solution, Jiří Váňa, Thibault Terencio, Vladimir Petrović, Orsolya Tischler, Zoltán Novák, Jana Roithová, Organometallics 2017, 36, 2072-2080. DOI: 10.1021/acs.organomet.6b00960 | [Full Text Link] [Supp. Info. Link, XYZ]

    We report a new method for determination of rate constants of processes in solution using electrospray ionization mass spectrometry (ESI-MS). The investigated reaction is C–H activation of acetanilides by palladium(II)trifluoroacetate leading to stable organopalladium complexes. The rate constants can be determined from an experiment with a couple of differently substituted acetanilides being in competition for being activated by the palladium salt. The formed organopalladium complexes can be detected by ESI-MS. The time dependence is achieved by adding one of the acetanilides to the reaction mixture with a time delay. The kinetics can be then evaluated from the evolution of the ratio of the ESI-MS signals of differently substituted complexes as a function of the time delay. The Hammett analysis of the rate constants obtained for a series of meta- and para-substituted acetanilides provides a ρ value of −1.5, which is in agreement with values reported for similar C–H activations. We have also investigated the very same reaction with UV–vis spectroscopy that gave us about three times smaller rate constants but the same trend with the ρ value of −1.6. The rate constants determined by ESI-MS are directly linked to the occurrence of organopalladium complexes, whereas the UV–vis data are associated with an absorption spectra change that could involve more reaction steps. DFT calculations support the interpretation of the reaction mechanism as cyclopalladation and provide the ρ value in the same range. The rate-determining step corresponds to the agostic C–H transition structure.

    zng pub 61

    Written on Thursday, 01 June 2017 14:48
  • 60. Hexafluorosilicic Acid as a Novel Reagent for the Desilylation of Silylacetylenes: Application in Sequential Sonogashira Coupling and Click Reaction

    Hexafluorosilicic Acid as a Novel Reagent for the Desilylation of Silylacetylenes: Application in Sequential Sonogashira Coupling and Click Reaction, Ádám Sinai, Ádám Mészáros, Ádám Balogh, Márton Zwillinger, Zoltán Novák, Synthesis 2017, 49, 2374-2388. DOI: 10.1055/s-0036-1588981 | [Full Text Link] [Supp. Info. Link]

    Key words: alkynes - azides - cycloaddition - click reaction - cross-coupling­ - fluoride - palladium - heterocycles

    Hexafluorosilicic acid was utilized as a novel, cheap, readily available, and environmentally benign alternative reagent for the desilylation of 1-trimethylsilylacetylenes. The applicability of the aqueous solution of the hexafluorosilicic acid was demonstrated in the sequential coupling of aryl halides and ethynyltrimethylsilane to afford internal acetylenes, benzofurans, and triazoles in one-pot Sonogashira–Sonogashira­ and Sonogashira–CuAAC reactions.

    zng pub 60

    Written on Thursday, 30 March 2017 13:49
  • 59. Gold-Catalyzed Direct Alkynylation of Azulenes

    Gold-Catalyzed Direct Alkynylation of Azulenes, Anna Székely, Áron Péter, Klára Aradi, Gergely L. Tolnai, Zoltán Novák, Org. Lett. 201719, 954-957. DOI: 10.1021/acs.orglett.7b00259 | [Full Text Link] [Supp. Info. Link]

    A novel catalytic method for the direct C-H alkynylation of azulenes was developed. The gold catalyzed functionalization of this special carbacycle iwas achieved with hypervalent iodonium reagent TIPS-EBX under mild reaction conditions. With the aid of the developed procedure, several TIPS alkynylated azulene derivatives were synthesized bearing important func-tional groups for further functionalization.

    zng pub 59

    Written on Saturday, 04 February 2017 13:33
  • 58. Erythrosine B catalyzed visible-light photoredox arylation-cyclization of N-alkyl-N-aryl-2-(trifluoromethyl)acrylamides to 3-(trifluoromethyl)indolin-2-one derivatives

    Erythrosine B catalyzed visible-light photoredox arylation-cyclization of N-alkyl-N-aryl-2-(trifluoromethyl)acrylamides to 3-(trifluoromethyl)indolin-2-one derivatives, Zsombor Gonda, Ferenc Béke, Orsolya Tischler, Milán Petró, Zoltán Novák, Balázs L. Tóth, Eur. J. Org. Chem. 201715, 2112-2117. DOI: 10.1002/ejoc.201601493 | [Full Text Link] [Supp. Info. Link]

    Special Issue: Photoredox Catalysis

    3-Trifluoromethyl-indoline-2-one derivatives were prepared in a visible-light photocatalytic transformation of acrylamides. The arylation-ring closure was initiated by light induced aryl radical generation from aryl diazonium salts with the utilization of erythrosine B as novel organic photocatalyst.

     zng pub 58

    Written on Thursday, 19 January 2017 19:27
  • 57. Direct ortho-Trifluoroethylation of Aromatic Ureas by Palladium Catalyzed C-H activation: A Missing Piece of Aromatic Substitutions

    Direct ortho-Trifluoroethylation of Aromatic Ureas by Palladium Catalyzed C-H activation: A Missing Piece of Aromatic SubstitutionsSzabolcs Kovács, Balázs L. Tóth, Gábor Borsik, Tamás Bihari, Nóra V. May, András Stirling, Zoltán Novák, Adv. Synth. Catal. 2017, 359, 527-532. DOI: 10.1002/adsc.201601136 | [Full Text Link] [Supp. Info. Link]

    Abstract: Development of direct late-stage installation of alkyl groups into aromatic systems is an important and challenging task of current organic chemistry. In spite of the existing functionalization methods in organic chemistry for the substitution reactions on aromatic systems, the direct alkylation of aromatic ureas is unknown. Herein, as a first example we report a novel palladium catalyzed fluoroalkylation process by C−H activation for the access of ortho trifluoroethylated aromatic ureas. The application of novel, highly active trifluoroethyl(mesityl)iodonium salt enables the efficient introduction of the trifluoroethyl group at 25 °C in 3 hours in high yields (up to 95%) with good functional group tolerance. DFT calculations have revealed a rate determining oxidative alkyl-group transfer preceded by an unexpected C−H activation route on the Pd center during the catalytic cycle, where the deprotonation is assisted by an external triflate anion.

    zng pub 57

    Written on Friday, 16 December 2016 16:39
  • 56. Study of Lewis Acid Accelerated Palladium Catalyzed C-H Activation

    Study of Lewis Acid Accelerated Palladium Catalyzed C-H Activation, Orsolya Tischler, Szabolcs Kovács, Gábor Érsek, Péter Králl, János Daru, András Stirling, Zoltán Novák, J. Mol. Catal. Chem. 2017, 426, 444-450. DOI: 10.1016/j.molcata.2016.09.018

    This paper is dedicated to Professor Georgiy B. Shul’pin on the occasion of his 70th birthday.

    Keywords
    C-H activation; palladium; Lewis acid; DFT studies

    Highlights
    •Amide and urea directed ortho-acylation and ortho-olefination on aromatic cores is accelerated by Lewis acidic additives.
    •Lewis acidic additives afford more electrophilic transition metal center, favoring C-H activation.
    •The efficiency of several palladium(II) catalysts is raised.
    •KIE experiments and calculations suggests a rate-determining C-H activation step.

    Abstract
    Acceleration of palladium catalyzed C-H activation by various Lewis Acids was demonstrated on the directed ortho-alkenylation and acylation of acetanilide and urea derivatives. The universality of this effect was investigated by the study of different palladium catalysts, directing groups in the aromatic substrates and versatile Lewis acids. Experiments were carried out to monitor the reactions and to compare the behavior and activity of different types of Lewis acids. Kinetic investigation revealed a rate determining C-H activation step, and DFT studies were performed for the explanation of Lewis acid effect on C-H activation.

    zng pub 56

    Written on Friday, 16 September 2016 14:59
  • 55. Mild Palladium Catalyzed ortho C-H Bond Functionalizations of Aniline Derivatives

    Mild Palladium Catalyzed ortho C-H Bond Functionalizations of Aniline Derivatives, Orsolya Tischler, Balázs L. Tóth, Zoltán Novák, Chem. Rec. 2017, 17, 184-199. DOI: 10.1002/tcr.201600059 | [Full Text Link]

    This account collects the developments and transformations which avoid the utilization of harsh reaction conditions in the field of palladium catalyzed, ortho-directed C-H activation of aniline derivatives from the first attempts to up-to-date results, including the results of our research laboratory. The discussed functionalizations performed under mild conditions include acylation, olefination, arylation, alkylation, alkoxylation reactions. Beside the optimization studies and the synthetic applications mechanistic investigations are also presented.

    zng pub 53

    Written on Thursday, 11 August 2016 15:15

2016

  • 54. Continuous flow synthesis of heterocyclic scaffolds Design principles of multistep systems – A review

    Continuous flow synthesis of heterocyclic scaffolds. Design principles of multistep systems – A review, Klára Lövei, Péter Bana, Róbert Örkényi, György I. Túrós, János Éles, Zoltán Novák, Ferenc Faigl, Chim. Oggi Chem. Today, 2016, 34, 18-21. Link

    KEYWORDS: Continuous flow synthesis, condensed heterocycles, scaffold, multistep flow synthesis, telescoping.

    ABSTRACT: The synthesis of novel heterocycles is an essential task in small-molecule drug discovery. Continuous flow processing opens the way for a new paradigm in laboratory-scale synthesis as well as pharmaceutical manufacturing. Based on our experiences with the multistep synthesis of condensed benzothiazoles, we gathered some of the key design features in light of literature examples.

    Written on Friday, 16 September 2016 14:49
  • 53. Recent advances in dual transition metal–visible light photoredox catalysis

    Recent advances in dual transition metal–visible light photoredox catalysisBalázs L. Tóth, Orsolya Tischler,  Zoltán Novák, Tetrahedron Lett. 2016, 57, 4505–4513. DOI: 10.1016/j.tetlet.2016.08.081 |

    In this Digest Letter, we collected and shortly summarized the recently developed dual transition metal–visible light photoredox catalytic processes including arylation, alkynylation, alkenylation, allylation, alkylation, fluoroalkylation, benzylation, acylation, and cyclization reactions. The utilization of multimetallic catalytic systems provides new synthetic strategies for the synthesis and functionalization of versatile and novel organic compounds.

     zng pub 54

    Written on Tuesday, 30 August 2016 20:41
  • 52. Understanding and Exploitation of Neighboring Heteroatom Effect for the Mild N‑Arylation of Heterocycles with Diaryliodonium Salts under Aqueous Conditions: A Theoretical and Experimental Mechanistic Study

    Understanding and Exploitation of Neighboring Heteroatom Effect for the Mild N‑Arylation of Heterocycles with Diaryliodonium Salts under Aqueous Conditions: A Theoretical and Experimental Mechanistic Study, Tamás Bihari, Bence Babinszki, Zsombor Gonda, Szabolcs Kovács, Zoltán Novák, András Stirling, J. Org. Chem. 2016, 81, 5417-5422. DOI: 10.1021/acs.joc.6b00779 | [Full Text Link] [Supp. Info. Link]

    The mechanism of arylation of N-heterocycles with unsymmetric diaryliodonium salts is elucidated. The fast and efficient N-arylation reaction is interpreted in terms of the bifunctionality of the substrate: The consecutive actions of properly oriented Lewis base and Brønsted acid centers in sufficient proximity result in the fast and efficient N-arylation. The mechanistic picture points to a promising synthetic strategy where suitably positioned nucleophilic and acidic centers enable functionalization, and it is tested experimentally.

    zng pub 52

    Written on Thursday, 16 June 2016 11:52
  • 51. Diaryliodonium Salts in Organic Syntheses: A Useful Compound Class for Novel Arylation Strategies

    Diaryliodonium Salts in Organic Syntheses: A Useful Compound Class for Novel Arylation Strategies, Klára Aradi, Balázs L. Tóth, Gergely L. Tolnai, Zoltán Novák, Synlett 2016, 27, 1456-1485. DOI: 10.1055/s-0035-1561369 | [Full Text Link]

    Keywords: arylation - diaryliodonium salts - hypervalent iodine reagents - metal-free - copper-catalyzed - palladium-catalyzed - C–H activation - direct functionalization

    This account aims to give a description of the usefulness of diaryliodonium salts in organic chemistry, including their synthesis and applications in the presence and absence of transition-metal catalysts. Herein, we briefly summarize the structural properties and reactivity of diaryliodonium salts. We describe several applications of these hypervalent reagents including metal-free arylations of C-, O-, N- and S-nu­cleophiles. The synthesis and functionalization of aromatic and heteroaromatic systems via copper- and palladium-catalyzed transformations are also discussed in this account.

    zng pub 51

    Content:

    1 Introduction
    2 Structural Properties and Reactivity
    3 Applications of Diaryliodonium Salts in Organic Syntheses
    3.1 Transition-Metal-Free Arylations of Heteroatom and Carbon Nucleophiles
    3.1.1 Arylation of Oxygen Nucleophiles
    3.1.1.1 Arylation of (Hetero)aromatic Alcohols
    3.1.1.2 Arylation of Aliphatic Alcohols
    3.1.1.3 Arylation of Acids
    3.1.2 Arylation of Nitrogen Nucleophiles
    3.1.2.1 N-Arylation of Amines and Amides
    3.1.2.2 N-Arylation of Heterocycles
    3.1.3 Arylation of Sulfur Nucleophiles
    3.1.4 Arylation of Inorganic Anions
    3.1.5 Arylation of Carbon Nucleophiles
    3.1.5.1 Electron-Rich Heterocycles
    3.1.5.2 Arylation of Carbonyl and Nitro Compounds
    3.2 Synthesis and Functionalization of Aromatic and Heteroaromatic Molecules with Diaryliodonium Salts in the Presence of Copper and Palladium Catalysts
    3.2.1 C–H Functionalizations by Copper-Catalyzed C–H Arylations
    3.2.2 Copper-Catalyzed Cyclization of Unsaturated Compounds with Diaryliodonium Salts
    3.2.3 Palladium-Catalyzed Arylations
    3.2.3.1 Electrophilic Palladation and Arylation
    3.2.3.2 Directing-Group-Assisted C–H Bond Activation and Arylation
    4 Conclusion

    Written on Wednesday, 02 March 2016 15:52
  • 50. Activation of C–H Activation: The Beneficial Effect of Catalytic Amount of Triaryl Boranes on Palladium-Catalyzed C–H Activation

    Activation of C–H Activation: The Beneficial Effect of Catalytic Amount of Triaryl Boranes on Palladium-Catalyzed C–H Activation, Orsolya Tischler, Zsófia Bokányi, Zoltán Novák, Organometallics 2016, 35, 741-746. DOI: 10.1021/acs.organomet.5b01017 | [Full Text Link] [Supp. Info. Link]

    Herein we report a novel approach to the acceleration of palladium-catalyzed C–H activation reactions. We demonstrated that the utilization of electron-deficient triaryl boranes as Lewis acidic cocatalysts of palladium enables the directed cross dehydrogenative coupling of aldehydes and anilides under mild reaction conditions. Study of the kinetic profile of the transformation reveals a unique, unexpectedly long induction period of the transformation.

    zng pub 50

    Written on Wednesday, 02 March 2016 08:32
  • 49. Mild and Efficient Palladium-Catalyzed Direct Trifluoroethylation of Aromatic Systems by C-H Activation

    Mild and Efficient Palladium-Catalyzed Direct Trifluoroethylation of Aromatic Systems by C-H Activation, Balázs L. Tóth, Szabolcs Kovács, Gergő Sályi, Zoltán Novák, Angew. Chem. Int. Ed. 2016, 55, 1988-1992. DOI: 10.1002/anie.201510555 | [Full Text Link] [Supp. Info. Link]

    The introduction of trifluoroalkyl groups into aromatic molecules is an important transformation in the field of organic and medicinal chemistry. However, the direct installation of fluoroalkyl groups onto aromatic molecules still represents a challenging and highly demanding synthetic task. Herein, a simple trifluoroethylation process that relies on the palladium-catalyzed C-H activation of aromatic compounds is described. With the utilization of a highly active trifluoroethyl(mesityl)iodonium salt, the developed catalytic method enables the first highly efficient and selective trifluoroethylation of aromatic compounds. The robust catalytic procedure provides the desired products in up to 95 % yield at 25 °C in 1.5 to 3 hours and tolerates a broad range of functional groups. The utilization of hypervalent reagents opens new synthetic possibilities for direct alkylations and fluoroalkylations in the field of transition-metal-catalyzed C-H activation.

    zng pub 49

    Simple: Anilides can be trifluoroethylated with a 2,2,2-trifluoroethyl-substituted iodonium salt in the presence of a palladium catalyst under mild conditions (see scheme). The reaction proceeds by CH activation at the ortho position and features a broad substrate scope.

    Frontispiece: Mild and Efficient Palladium-Catalyzed Direct Trifluoroethylation of Aromatic Systems by C−H Activation, DOI: 10.1002/anie.201680661

    Trifluoroethylation In their Communication on page 1988 ff., Z. Novák and co-workers describe the use of a trifluoroethyl(mesityl)iodonium salt for the simple and efficient palladium-catalyzed trifluoroethylation of aromatic compounds by C−H activation.

    Written on Thursday, 14 January 2016 16:56
  • 48. Modular Copper-Catalyzed Synthesis of Chromeno[4,3-b]quinolines with the Utilization of Diaryliodonium Salts

    Modular Copper-Catalyzed Synthesis of Chromeno[4,3-b]quinolines with the Utilization of Diaryliodonium Salts, Klára Aradi, Petra Bombicz, Zoltán Novák, J. Org. Chem. 2016, 81, 920-931. DOI: 10.1021/acs.joc.5b02490 | [Full Text Link] [Supp. Info. Link, CIF]

    A novel, highly modular synthetic method with high functional group tolerance was developed for the construction of chromenoquinoline derivatives from arylpropynyloxy-benzonitriles and diaryliodonium triflates via an oxidative arylation–cyclization path. The copper(I) chloride catalyzed reaction is presumed to involve the formation of highly active arylcopper(III) species.

    zng pub 48

    Written on Monday, 11 January 2016 13:14

2015

  • 47. Transition-Metal-Free N-Arylation of Pyrazoles with Diaryliodonium Salts

    Transition-Metal-Free N-Arylation of Pyrazoles with Diaryliodonium Salts, Zsombor Gonda, Zoltán Novák, Chem. Eur. J.  2015, 21, 16801-16806. DOI: 10.1002/chem.201502995 | [Full Text Link] [Supp. Info. Link]

    A new synthetic method was developed for the N-arylation of pyrazoles using diaryliodonium salts. The transformation does not require any transition-metal catalyst and provides the desired N-arylpyrazoles rapidly under mild reaction condition in the presence of aqueous ammonia solution as a mild base without the use of inert atmosphere. The chemoselectivity of unsymmetric diaryliodonium salts was also explored with large number of examples.

    zng pub 47

    Written on Tuesday, 06 October 2015 08:15
  • 46. Utilization of Copper-Catalyzed Carboarylation–Ring Closure for the Synthesis of New Oxazoline Derivatives

    Utilization of Copper-Catalyzed Carboarylation–Ring Closure for the Synthesis of New Oxazoline Derivatives, Ádám Sinai, Dóra Vangel, Tamás Gáti, Petra Bombicz, Zoltán Novák, Org. Lett. 2015, 17, 4136-4139. DOI: 10.1021/acs.orglett.5b01860 | [Full Text Link] [Supp. Info. LinkCIF]

    A copper-catalyzed carboarylation–ring-closure strategy was used for the modular synthesis of oxazolines via the reaction of 1-aryl- and 1-alkylpropargylamides and diaryliodonium salts. The novel approach enables the efficient, modular synthesis of oxazoline derivatives bearing fully substituted exo double bonds.

    zng pub 46

    Written on Monday, 24 August 2015 09:57
  • 45. Multistep Continuous-Flow Synthesis of Condensed Benzothiazoles

    Multistep Continuous-Flow Synthesis of Condensed Benzothiazoles, Klára Lövei, István Greiner, János Éles, Áron Szigetvári, Miklós Dékány, Sándor Lévai, Zoltán Novák, György István Túrós, J. Flow Chem. 2015, 5, 74–81. DOI10.1556/1846.2015.00004 | [Full Text Link[Supp. Info Link]

    In medicinal chemistry, the development of synthetic procedures for the access of new heterocyclic systems as potential scaffolds is elementary. Herein, we report our results on the formation of small drug-like heterocycles, utilizing flow chemistry. This approach enables the extension of the reaction parameter window, including high-pressure/high-temperature or hazardous chemistry. In our work, various novel condensed tricyclic benzothiazoles fused with furo- and thieno-rings were synthesized applying a multistep continuous-flow protocol. The process includes two ring closure steps and a nitro group reduction step. Batch and telescoped continuous-flow syntheses were also designed and performed.

    Written on Monday, 06 July 2015 13:21
  • 44. Efficient Direct 2,2,2-Trifluoroethylation of Indoles via C-H Functionalization

    Efficient Direct 2,2,2-Trifluoroethylation of Indoles via C-H Functionalization, Gergely László Tolnai, Anna Székely, Zita Makó, Tamás Gáti, János Daru, Tamás Bihari, Andras Stirling and Zoltán Novák, Chem. Commun. 201551, 4488-4491. DOI10.1039/C5CC00519A | [Supp. Info Link]

    A novel highly C3 selective metal free trifluoroethylation of indoles using 2,2,2-trifuoroethyl(mesityl)-iodonium triflate was developed. The methodology enables the introduction of a trifluoroethyl group in a fast and efficient reaction under mild conditions with high functional group tolerance. Beyond the synthetic developments, quantum chemical calculations provide a deeper understanding of the transformation.

    zng pub 44

    Written on Sunday, 22 February 2015 15:56
  • 43. Copper-Catalyzed Oxidative Ring Closure of ortho-Cyanoanilides with Hypervalent Iodonium Salts: Arylation–Ring Closure Approach to Iminobenzoxazines

    Copper-Catalyzed Oxidative Ring Closure of ortho-Cyanoanilides with Hypervalent Iodonium Salts: Arylation–Ring Closure Approach to Iminobenzoxazines, Klára Aradi, Zoltán Novák, Adv. Synt. Catal. 2015357, 371-376. DOI: 10.1002/adsc.201400763 | [Full Text Link[Supp. Info Link]

    A novel, highly modular synthetic methodology with high functional group tolerance was developed for the construction of iminobenzoxazine derivatives from ortho-cyanoanilides and diaryliodonium triflates via an oxidative arylation–cyclization path. The reaction is supposed to involve the formation of highly active aryl-copper(III) species. In this novel transformation, copper(II) triflate was used as catalyst in 1,2-dichloroethane or ethyl acetate and the reaction takes place at 75 °C in 2–16 h.

    zng pub 43

     

    Written on Sunday, 22 February 2015 15:56

2014

  • 42. Synthesis and Transformations of Oxygen Heterocycles

    Synthesis and Transformations of Oxygen Heterocycles, Zoltán Novák, András Kotschy, Topics in Heterocyclic Chemistry Vol. 45, 231-303. DOI: 10.1007/7081_2014_136

    The recent developments in the transition metal-catalyzed synthesis and transformations of such oxygen-containing heteroaromatic systems are reviewed, where the oxygen is part of a five-membered ring.

    zng pub 42

     

    Written on Sunday, 22 February 2015 15:56
  • 41. Mechanistic Study of Silver-Mediated Furan Formation by Oxidative Coupling

    Mechanistic Study of Silver-Mediated Furan Formation by Oxidative Coupling, János Daru, Zsuzsanna Benda, Ádám Póti, Zoltán Novák,  András Stirling, Chem. Eur. J. 2014, 20, 15395–15400. DOI: 10.1002/chem.201404302 | [Full Text Link[Supp. Info Link]

    Density functional calculations and experiments have been carried out to unravel the mechanism of a silver-mediated furan formation by oxidative coupling. Various possible reaction paths were considered and the most favorable channel has been identified on the basis of the calculated solvent-corrected Gibbs free-energy profiles. The mechanism represented by this route consists of a radical and a subsequent ionic route. The silver cation has a double role in the mechanism: it is the oxidant in the radical steps and the catalyst for the ionic steps, which is in accordance with the experimental observations. The two most important aspects of the optimal route are the formation of a silver–acetylide, reacting subsequently with the enolate radical, and the aromatic furan-ring formation in a single step at the latter, ionic segment of the reaction path. Our findings could explain several experimental observations, including the “key-promoter role” of silver, the preference for ionic cyclization, and the reduced reactivity of internal acetylides.

    zng pub 41

    Written on Sunday, 22 February 2015 15:56
  • 40. Continuous-flow azide–alkyne cycloadditions with an effective bimetallic catalyst and a simple scavenger system

    Continuous-flow azide–alkyne cycloadditions with an effective bimetallic catalyst and a simple scavenger system, Sándor B. Ötvös, Gábor Hatoss, Ádám Georgiádes, Szabolcs Kovács, István M. Mándity, Zoltán Novák, Ferenc Fülöp, RSC Adv. 2014, 4, 46666-46674. DOI: 10.1039/C4RA07954J | [Supp. Info Link]

    A flow chemistry-based technique is presented herein for Cu(I)-catalyzed azide–alkyne cycloadditions with a copper on iron bimetallic system as the catalyst and iron powder as a readily available copper scavenger. The method proved to be rapid and safe as compared with the conventional batch experiment; and by using an in-line copper scavenger, the level of copper impurities in the triazole products could readily be reduced to negligibly small amounts. The process was widely applicable, as not only terminal alkynes, but also various disubstituted acetylenes were nicely tolerated as dipolarophiles leading to useful 1,4,5-trisubstituted 1,2,3-triazoles.

    zng pub 40

    Written on Sunday, 22 February 2015 15:56
  • 39. Efficient Copper-Catalyzed Trifluoromethylation of Aromatic and Heteroaromatic Iodides: The Beneficial Anchoring Effect of Borates

    Efficient Copper-Catalyzed Trifluoromethylation of Aromatic and Heteroaromatic Iodides: The Beneficial Anchoring Effect of Borates, Zsombor Gonda, Szabolcs Kovács, Csaba Wéber, Tamás Gáti, Attila Mészáros, András Kotschy, Zoltán Novák, Org. Lett. 2014, 16, 4268-4271. DOI: 10.1021/ol501967c | [Full Text Info] [Supp. Info Link, NMR]

    Efficient copper-catalyzed trifluoromethylation of aromatic iodides was achieved with TMSCF3 in the presence of trimethylborate. The Lewis acid was used to anchor the in situ generated trifluoromethyl anion and suppress its rapid decomposition. Broad applicability of the new trifluoromethylating reaction was demonstrated in the functionalization of different aromatic and heteroaromatic iodides.

    zng pub 39

    Written on Sunday, 23 November 2014 00:00
  • 38. Utilization of a Copper on Iron Catalyst for the Synthesis of Biaryl Systems and Benzoxazines via Oxidative Arylation of Anilide Derivatives

    Utilization of a Copper on Iron Catalyst for the Synthesis of Biaryl Systems and Benzoxazines via Oxidative Arylation of Anilide Derivatives, Anna Székely, Ádám Sinai, Edina B. Tóth, Zoltán Novák, Synthesis 2014, 14, 1871-1880. DOI: 10.1055/s-0033-1338642 | [Full Text Link[Supp. Info Link]

    Heterogeneous copper on iron catalyst serves as an efficient alternative copper source for arylation reactions using hypervalent iodonium salts. The copper(0) catalyst affords meta-arylation of pivalanilides, while 2-ethynylanilides undergo oxidative carbo­arylation–ring closure with diaryliodonium salts.

    zng pub 38

    Written on Sunday, 23 November 2014 00:00
  • 37. Palladium-Catalyzed Methoxylation of Aromatic Chlorides with Borate Salts

    Palladium-Catalyzed Methoxylation of Aromatic Chlorides with Borate Salts, Gergely L. Tolnai, Bálint Pethő, Péter Králl, Zoltán Novák, Adv. Synth. Catal. 2014, 356, 125-129. DOI: 10.1002/adsc.201300687 | [Full Text Link[Supp. Info Link]

    Herein we disclose a simple palladium-catalyzed transformation for the methoxylation of aromatic chlorides with tetramethoxyborate salts. The procedure provides a new and efficient synthetic tool for the introduction of a methoxy group into aromatic systems. In addition, the reaction can be achieved using a wide range of aromatic and heteroaromatic chlorides, the cheapest class of halides.

    zng pub 37

    Written on Sunday, 23 November 2014 00:00
  • 36. A one-pot process for palladium catalyzed direct C-H acylation of anilines in water using a removable ortho directing group

    A one-pot process for palladium catalyzed direct C-H acylation of anilines in water using a removable ortho directing group ,Fruzsina Szabó, Dániel Simkó, Zoltán Novák, RSC Advances 2014, 4, 3883-3886. DOI: 10.1039/C3RA45160G | [Supp. Info Link]

    A new mild, practical method for the synthesis of aminobenzophenone derivatives through a three step one-pot reaction sequence involving acylation of anilines, palladium catalyzed cross-dehydrogenative coupling of the formed anilides and the hydrolytic cleavage is reported. The full reaction sequence was performed under aqueous conditions.

    zng pub 36

    Written on Sunday, 23 November 2014 00:00

2013

2012

  • 31. Copper on Iron: Catalyst and Scavanger for Azide-Alkzne Cycloaddition

    Copper on Iron: Catalyst and Scavanger for Azide-Alkzne Cycloaddition, Szabolcs Kovács, Katalin Zih-Perényi, Ádám Révész, Zoltán Novák, Synthesis 2012; 44, 3722-3730. DOI: 10.1055/s-0032-1317697 | [Full Text Link[Supp. Info Link]

    Dipolar cycloaddition of terminal alkynes and azides catalyzed by the Cu/Fe bimetallic system is reported. In the presence of a readily accessible nanosized copper source, the cycloaddition reaction can be easily achieved at ambient temperature with high efficiency. The product obtained from the reaction catalyzed by Cu/Fe contains significantly lower copper contaminants compared to various active homogeneous copper complexes. Iron not only behaves as support for copper, but acts as a redox scavenger, and reduces the copper contamination of the organic product.

    zng pub 31

    Written on Sunday, 23 November 2014 00:00
  • 30. Design and Application of New Imidazolylsulfonate-Based Benzyne Precursor: An Efficient Triflate Alternative

    Design and Application of New Imidazolylsulfonate-Based Benzyne Precursor: An Efficient Triflate Alternative, Szabolcs Kovács, Ádám I. Csincsi, Tibor Zs. Nagy, Sándor Boros, Géza Timári, Zoltán Novák, Org. Lett. 2012, 14, 2022-2025. DOI: 10.1021/ol300529j | [Full Text Link[Supp. Info Link]

    Several o-(trimethylsilyl)aryl imidazolylsulfonates were synthesized in a simple process and successfully applied in cycloadditions involving benzyne intermediates. The precursor offers an efficient alternative for generating benzynes compared to widely used ortho TMS triflates under similar reaction conditions. With the utilization of this new precursor, the formation of potentially genotoxic trifluoromethanesulfonate side product is eliminated. The applicability of the new benzyne precursor was demonstrated in different types of cycloaddition reactions to prepare heterocyclic molecules.

    zng pub 30

    Written on Sunday, 23 November 2014 00:00
  • 29. Evaluation of bis-triphenylphosphano-copper(I)-butyrate (C3H7COOCu(PPh3)2) as catalyst for the synthesis of 1-(D-glycopyranosyl)-4-substituted-1,2,3-triazoles

    Evaluation of bis-triphenylphosphano-copper(I)-butyrate (C3H7COOCu(PPh3)2) as catalyst for the synthesis of 1-(D-glycopyranosyl)-4-substituted-1,2,3-triazoles, Éva Bokor, Csenge Koppány, Zsombor Gonda, Zoltán Novák, László Somsák, Carbohydr. Res. 2012, 351, 42-48. DOI: 10.1016/j.carres.2012.01.004 | [Full Text Link]

    Bis-triphenylphosphano-copper(I)-butyrate (C3H7COOCu(PPh3)2) was applied for the synthesis of O-peracylated 1-glycopyranosyl-4-substituted-1,2,3-triazoles from the corresponding glycosyl azides and alkynes. This catalyst proved superior to the CuSO4/l-ascorbic acid system even with sterically hindered and less reactive glycosyl azides.

    zng pub 29

    Written on Sunday, 23 November 2014 00:00

2011

  • 28. Enantioselective Decarboxylative Alkylation Reactions: Catalyst Development, Substrate Scope, and Mechanistic Studies

    Enantioselective Decarboxylative Alkylation Reactions: Catalyst Development, Substrate Scope, and Mechanistic Studies, Douglas C. Behenna, Justin T. Mohr,Nathaniel H. Sherden, Smaranda C. Marinescu, Andrew M. Harned, Kousuke Tani, Masaki Seto, Sandy Ma, Zoltán Novák, Michael R. Krout, Ryan M. McFadden, Jennifer L. Roizen, John A. Enquist Jr., David E. White, Samantha R. Levine, Krastina V. Petrova, Akihiko Iwashita, Scott C. Virgil, Brian M. Stoltz, Chem. Eur. J. 2011, 17, 14199-14223. DOI: 10.1002/chem.201003383 | [Full Text Link[Supp. Info Link]

    α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center.

    zng pub 28

    Written on Sunday, 23 November 2014 00:00
  • 27. N-Halosuccinimide/SiCl4 as general, mild and efficient systems for the α-monohalogenation of carbonyl compounds and for benzylic halogenation

    N-Halosuccinimide/SiCl4 as general, mild and efficient systems for the α-monohalogenation of carbonyl compounds and for benzylic halogenation, Tarek A. Salama, Zoltán Novák, Tetrahedron Lett. 2011, 52, 4026-4029. DOI: 10.1016/j.tetlet.2011.05.135 |

    Combinations of N-halosuccinimide and tetrachlorosilane in acetonitrile were found to be efficient systems for the selective α-monohalogenation of carbonyl compounds as well as for benzylic halogenation under mild conditions.

    zng pub 27

    Written on Sunday, 23 November 2014 00:00
  • 26. Oxidoreductive Coupling of Thiols with Aryl Halides Catalyzed by Copper on Iron

    Oxidoreductive Coupling of Thiols with Aryl Halides Catalyzed by Copper on Iron, Szabolcs Kovács, Zoltán Novák, Org. Biomol. Chem. 2011, 9, 711-716. DOI: 10.1039/C0OB00397B | [Supp. Info Link]

    Synthesis and utilization of a simple copper on iron catalyst in the coupling of aryl halides with thiols through disulfide intermediate is reported. The iron support of copper catalyst ensures reductive media for the coupling, allows easy removal of the metals by outer magnetic field and enables the recycling of the catalyst.

    zng pub 26

    Written on Sunday, 23 November 2014 00:00

2010

  • 25. Efficient Synthesis of Deuterated 1,2,3-Triazoles

    Efficient Synthesis of Deuterated 1,2,3-Triazoles, Zsombor Gonda, Krisztán Lőrincz, Zoltán Novák, Tetrahedron Lett. 2010, 51, 6275-6277. DOI: 10.1016/j.tetlet.2010.09.097 | [Full Text Link]

    A wide variety of 1-monosubstituted 1,2,3-triazoles were synthesized efficiently via a copper-catalyzed click-reaction between azides and acetylene gas, generated in situ from CaC2 with the addition of H2O or D2O.

    zng pub 25

    Written on Sunday, 23 November 2014 00:00
  • 24. Dramatic Impact of ppb Levels of Palladium on the "Copper-Catalyzed" Sonogashira Coupling

    Dramatic Impact of ppb Levels of Palladium on the "Copper-Catalyzed" Sonogashira Coupling, Zsombor Gonda, Gergely L. Tolnai, Zoltán Novák, Chem. Eur. J. 2010, 16, 11822-11826. DOI: 10.1002/chem.201001880 | [Full Text Link[Supp. Info Link]

    Palladacadabra! The effect of ppb levels of palladium on the “copper-catalyzed” Sonogashira coupling is reported. The observed high sensitivity to palladium impurities queries the existence of pure copper catalysis in the coupling of aryl iodides and terminal acetylenes (see figure).

    zng pub 24

    Written on Sunday, 23 November 2014 00:00
  • 23. Activity of palladium on charcoal catalysts in cross-coupling reactions

    Activity of palladium on charcoal catalysts in cross-coupling reactions, Anna Komáromi, Fruzsina Szabó, Zoltán Novák, Tetrahedron Lett. 2010, 51, 5411-5414. DOI: 10.1016/j.tetlet.2010.07.170 |

    Comparison of the activity of several commercially available Pd/C catalysts in C–C, C–N, and C–S bond forming cross-coupling reactions has demonstrated the importance of the choice of the catalyst source. Investigations showed marked difference in activity between the catalysts. Moreover, the catalytic activity of each catalyst varies with respect to the coupling. The first Pd/C catalyzed Hiyama coupling is reported.

    zng pub 23

    Written on Sunday, 23 November 2014 00:00
  • 22. Examination of the Aromatic Amination Catalyzed by Palladium on Charcoal

    Examination of the Aromatic Amination Catalyzed by Palladium on Charcoal, Anna Komáromi, Zoltán Novák, Adv. Synth. Catal. 2010, 352, 1523. DOI: 10.1002/adsc.201000048 | [Full Text Link[Supp. Info Link]

    The Buchwald–Hartwig amination of aryl halides with secondary amines and functionalized aromatic amines catalyzed by solid-supported palladium is reported. The choices of ligand, base and solvent are crucial for the successful coupling. The amination of aromatic iodides, bromides and chlorides can be easily achieved with palladium on charcoal in the presence of a biphenylphosphane-type ligand at 80–110 °C. In addition, the palladium on charcoal catalyst is easily separable after the reaction, and reusable several times with only small activity loss.

    zng pub 22

    Written on Sunday, 23 November 2014 00:00
  • 21. Highly Active Copper Catalysts for Azide-Alkyne Cycloaddition

    Highly Active Copper Catalysts for Azide-Alkyne Cycloaddition, Zsombor Gonda, Zoltán Novák, Dalton Trans. 2010, 39, 726-729. DOI: 10.1039/b920790m | [Supp. Info Link]

    Bis-triphenylphosphano complexes of copper(I)-carboxylates serve as efficient catalysts for azide-alkyne cycloaddition. The triazole formation takes place straightforwardly at ambient temperature providing a wide variety of products with good yields in the presence of 0.005–0.05% catalyst.

    zng pub 21

    Written on Sunday, 23 November 2014 00:00

2009

2008

  • 19. Copper-free Sonogashira coupling in amine-water solvent mixtures

    Copper-free Sonogashira coupling in amine-water solvent mixtures, Anna Komáromi, Gergely L. Tolnai, Zoltán Novák, Tetrahedron Lett. 2008, 49, 7294-7298. DOI: 10.1016/j.tetlet.2008.10.037 |

    Extensive study of different amine–water solvent mixtures was carried out for copper free Sonogashira coupling of aryl iodides. The influence of the palladium sources, ligands, amine–water ratio and further additives was also evaluated. Application of sec-butylamine–water mixture proved to be an excellent medium for rapid and efficient coupling of aryl-iodides at ambient temperature in the presence of PdCl2(PPh3)2 as catalyst.

    zng pub 19

    Written on Sunday, 23 November 2014 00:00
  • 18. Efficient Copper-free Sonogashira Coupling of Aryl Chlorides with Palladium on Charcoal

    Efficient Copper-free Sonogashira Coupling of Aryl Chlorides with Palladium on Charcoal, Anna Komáromi, Zoltán Novák, Chem. Commun. 2008, 4968-4970. DOI: 10.1039/b810928a | [Supp. Info Link]

    Palladium on charcoal serves as an efficient and reusable solid supported catalyst for the Sonogashira coupling of aryl chlorides with terminal acetylenes in the presence of a bulky, electron-rich biphenyl type ligand (XPhos), without copper co-catalyst.

    zng pub 18

    Written on Sunday, 23 November 2014 00:00

Before the ZNG

  • 17. Development of a one-pot sequential Sonogashira coupling for the synthesis of benzofurans

    Development of a one-pot sequential Sonogashira coupling for the synthesis of benzofurans, Márton Csékei, Zoltán Novák, András Kotschy, Tetrahedron 2008, 64, 8992-8996. DOI10.1016/j.tet.2008.05.100 |

    An efficient one-pot protocol was developed for the construction of the benzofuran system from aryl halides and protected iodophenols using carbinol-based acetylene sources. The sequence includes alternating palladium-catalyzed Sonogashira couplings and deprotection steps concluded by a ring closure. The developed one-pot procedure was compared with the stepwise approach and its efficiency was also demonstrated by the total synthesis of vignafuran, a benzofuran natural product.

    Written on Wednesday, 19 November 2008 00:00
  • 16. Ethynyl-cyclohexanol: an efficient acetylene surrogate in Sonogashira coupling

    Ethynyl-cyclohexanol: an efficient acetylene surrogate in Sonogashira coupling, Márton Csékei, Zoltán Novák, András Kotschy, Tetrahedron 2008, 64, 975-982. DOI10.1016/j.tet.2007.10.031 |

    The Sonogashira coupling of aryl halides in the presence of 1-ethynyl-cyclohexanol as an acetylene source provides an efficient method for the synthesis of diarylacetylenes without the isolation of the appropriate arylacetylenes.

    Written on Wednesday, 19 November 2008 00:00
  • 15. Quinoidal Tetrazines: Formation of a Fascinating Compound Class

    Quinoidal Tetrazines:  Formation of a Fascinating Compound Class, Beatrix Bostai, Zoltán Novák, Attila C. Bényei, András Kotschy, Org. Lett. 2007, 9, 3437-3439. DOI: 10.1021/ol701442h | [Full Text Link] [Supp. Info Link, CIF]

    A series of different N-heterocyclic carbenes (NHCs) were reacted with 3,6-bis(3‘,5‘-dimethylpyrazolyl)-tetrazine in the presence of an inorganic carbonate to provide access to a hitherto unprecedented compound class. The formed tetrazine derivatives bearing the NHC in the 3-position and an oxygen in the 6-position show a quinoidal-like structure, according to physical examinations and X-ray crystallography.

    Written on Wednesday, 19 November 2008 00:00
  • 14. A multidimensional overpressured layer chromatographic method for the characterization of tetrazine libraries

    A multidimensional overpressured layer chromatographic method for the characterization of tetrazine libraries, Naran Gombusuren, Zoltán Novák, András Kotschy, E. Mincsovics, Gábor Dibó, J. Biochem. Biophys. Methods 2007, 69, 239-249. DOI10.1016/j.jbbm.2005.12.005 | [Full Text Link]

    The recent combinatorial approach in synthetic organic chemistry started a new age in drug discovery. The generation of compound libraries in combination with high-throughput screening has become the method of choice for the production of new pharmacological leads for chemical optimization. Characterization and separation of such pool of compounds have been lagging behind the synthetic and screening methodologies. Overpressured layer chromatography (OPLC) is an instrumentalized planar liquid chromatographic technique associated with the use of optimized layers prepared from particles of narrow particle size distribution and small diameter. On one hand, uni-directional OPLC allows the simultaneous separation of large number of samples in minutes. On the other hand, two-dimensional OPLC offers multidimensional separation on a single layer. This paper shows the complete multidimensional separation of a tetrazine library prepared by parallel combinatorial synthesis. In general, this approach may become the method of choice for the characterization of compound libraries.

    Written on Wednesday, 19 November 2008 00:00
  • 13. Oxidative Kinetic Resolution-Claisen Rearrangement Sequence to Enantio-enriched Arylcycloalkenes

    Oxidative Kinetic Resolution-Claisen Rearrangement Sequence to ­Enantioenriched Arylcycloalkenes, David C. Ebner, Zoltán Novák, Brian M. Stoltz, Synlett 2006, 20, 3533-3539. DOI: 10.1055/s-2006-958415 | [Full Text Link]

    The Pd-catalyzed oxidative kinetic resolution of secondary alcohols afforded enantioenriched allylic alcohols with high ­selectivity. These alcohols were transformed into arylcycloalkenes with enantioenriched tertiary and quaternary stereocenters through a two-step vinylation and Lewis acid promoted Claisen rearrangement. Subsequent Pd-catalyzed oxidative cyclization of a Claisen product afforded a 5,5-fused tetrahydrofuran.

    Written on Sunday, 19 November 2006 00:00
  • 12. Study of the formation and Thermal Decomposition of an Azo-Bridged Tricyclic Ring System

    Study of the Formation and Thermal Decomposition of an Azo-Bridged Tricyclic Ring System, Zoltán Novák, Zoltán Vincze, Zsuzsanna Czégény, Gábor Magyarfalvi, David M. Smith, András Kotschy, Eur. J. Org. Chem. 2006, 15, 3358-3363. DOI: 10.1002/ejoc.200600058 | [Full Text Link]

    1-Amino-2-methyl-1,3-pentadienes were treated with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate to give diazatricyclo[2.2.2.0]octenes and dimethyl 4-methylpyridazine-3,6-dicarboxylate, the product distribution being largely dependent on the nature of the amino substituent. Under similar conditions the analogous 1-morpholino-1,3-butadiene afforded dimethyl pyridazine-3,6-dicarboxylate as the major product. The tricyclic products underwent selective thermal decomposition to give dimethyl 4-methylpyridazine-3,6-dicarboxylate in excellent yield. The proposed mechanism of the formation as well as of the decomposition was supported by quantum chemical calculations and experimental evidence.

    Written on Sunday, 19 November 2006 00:00
  • 11. Sequential and domino Sonogashira coupling: Efficient tools for the synthesis of diarylalkynes

    Sequential and domino Sonogashira coupling: Efficient tools for the synthesis of diarylalkynes, András Nagy, Zoltán Novák, András Kotschy, J. Organomet. Chem. 2005, 690, 4453-4461. DOI10.1016/j.jorganchem.2004.12.036 |

    The Sonogashira coupling reaction of aryl halides with a masked acetylene, leading to the formation of diarylethynes is reviewed. The process is either run in a sequential coupling–deprotection–coupling manner, or sometimes it is carried out in one-pot, a reaction we coined domino coupling. The procedures were also extended to the synthesis of compound libraries.

    Written on Saturday, 19 November 2005 00:00
  • 10. Tandem Sonogashira coupling: an efficient tol for the synthesis of diarylalkynes

    Tandem Sonogashira Coupling: An Efficient Tool for the Synthesis of Diarylalkynes, Zoltán Novák, Péter Nemes, András Kotschy, Org. Lett. 2005, 6, 4917-4920. DOI10.1021/ol047983f | [Full Text Link] [Supp. Info Link]

    The tandem Sonogashira coupling reaction of aryl halides provides an efficient method for the synthesis of diarylalkynes. Several aryl halides were coupled with 2-methyl-3-butyn-2-ol as acetylene source in the presence of PdCl2(PPh3)2 and CuI. Following the deprotection of the acetylene moiety in the same pot using a strong base, the Sonogashira coupling of a second aryl halide led to the formation of the appropriate diarylakyne. The established protocoll was successfully extended to the preparation of compound libraries.

    Written on Saturday, 19 February 2005 00:00
  • 9. The "one-pot" preparation of substituted benzofurans

    The 'one-pot' preparation of substituted benzofurans, Márton Csékei, Zoltán Novák, Géza Timári, András Kotschy, Arkivoc 2004, 5, 285-291. (SA-1110BP) | [Full Text Link]

    A simple one-pot procedure has been elaborated for the preparation of substituted benzofurans starting from halogenated phenols, and this method has been applied successfully to the total synthesis of dehydrotremetone, a natural product of White Snakeroot.


    Keywords: Benzofurans, Sonogashira coupling, natural product, synthesis.

    Written on Friday, 19 November 2004 00:00
  • 8. The azaphilic addition of organometallic reagents on tetrazines: scope and limitations

    János Faragó, Zoltán Novák, Gitta Schlosser, Antal Csámpai, András Kotschy, Tetrahedron 2004, 60, 1991. DOI10.1016/j.tet.2004.01.013 |

    A series of tetrazines were reacted with organometallic reagents. Depending on the nature of the metal azaphilic addition, reduction of the tetrazine or simple complex formation was the predominant transformation and usually high selectivity was observed.

    Written on Friday, 19 November 2004 00:00
  • 7. Correlation of the chemical reactivity of some tetrazine derivatives with their reactivity towards ortho-positronium atoms and their LUMO energies

    Correlation of the Chemical Reactivity of Some Tetrazine Derivatives with Their Reactivity toward Ortho-positronium Atoms and Their LUMO Energies, András Kotschy, Zoltán Novák, Béla Lévay, J. Phys. Chem. A 2004, 108, 1753-1756. DOI10.1021/jp0373649 | [Full Text Link]

    Chemical reaction rate constants of the nucleophilic ortho-positronium (o-Ps) atom with a series of tetrazine derivatives were determined in dimethylformamide (DMF) solutions by positron annihilation lifetime spectroscopy. The observed rate constants are in the range that corresponds to that of the diffusion-controlled reactions. It was shown that this pronounced reactivity of tetrazines toward o-Ps stems from the electron-deficient tetrazine core. The introduction of electron-donating substituents onto the tetrazine ring, as expected, decreases the reactivity of the molecule toward o-Ps. The measured reaction rate constants of o-Ps resulted in a good linear correlation with the calculated LUMO energies of the tetrazines. The reactivity of tetrazines toward o-Ps correlated well also with their reactivity toward classical nucleophiles.

    Written on Friday, 19 November 2004 00:00
  • 6. Selective Nucleophilic Substitutions on Tetrazines

    Selective Nucleophilic Substitutions on Tetrazines, Zoltán Novák, Beatrix Bostai, Márton Csékei, Krisztián Lőrincz, András Kotschy, Heterocycles 2003, 60, 2653-2668. DOI: 10.3987/COM-03-9875 | [Full Text Link]

    A series of tetrazine derivatives bearing a leaving group were reacted with different nucleophiles to undergo either the expected substitution reaction or an unexpected exchange of the other substituent of the tetrazine ring selectively. The influence of the choice of nucleophile as well as the substituents on the tetrazine was examined in detail and the interpretation of the results was also supported by quantum chemical calculations.

    Written on Wednesday, 19 November 2003 00:00
  • 5. The first cross-coupling reactions on tetrazines

    First Cross-Coupling Reactions on Tetrazines, Zoltán Novák, András Kotschy, Org. Lett. 2003, 5, 3495-3497. DOI: 10.1021/ol035312w | [Full Text Link] [Supp. Info Link]

    A series of substituted chlorotetrazines were reacted with different terminal alkynes under Sonogashira or Negishi coupling conditions to furnish alkynyl-tetrazines in good to moderate yield. The electron-donating properties of the substituent on the tetrazine core were found to have a significant influence on the success of the reaction. These results constitute the first cross-coupling reactions on tetrazines.

    Written on Wednesday, 19 November 2003 00:00
  • 4.The first total synthesis of Cicerfuran utilizing a one-pot synthesis of hydroxylated benzofuranes

    The first total synthesis of Cicerfuran utilizing a one-pot synthesis of hydroxylated benzofuranes, Zoltán Novák, Géza Timári, András Kotschy, Tetrahedron 2003, 59, 7509-7513. DOI10.1016/S0040-4020(03)01170-0 |

    A simple one-pot procedure was elaborated for the preparation of hydroxylated benzofurans from halogenated phenols and was successfully applied to the first total synthesis of Cicerfuran, a natural defence agent of wild chickpea.

    Written on Wednesday, 19 November 2003 00:00
  • 3. Sonogashira Coupling of Aryl Halides Catalyzed by Palladium on Charcoal

    Sonogashira Coupling of Aryl Halides Catalyzed by Palladium on Charcoal, Zoltán Novák, András Szabó, József Répási, András Kotschy, J. Org. Chem. 2003, 68, 3327-3329. DOI: 10.1021/jo034149f | [Full Text Link] [Supp. Info Link]

    With the proper choice of solvent, palladium on charcoal acts as an efficient catalyst in the Sonogashira cross-coupling reaction of aryl bromides. The catalytically active species in the process is probably palladium, which leaches into the solution but returns onto the surface of the charcoal at the end of the reaction.

    Written on Wednesday, 19 November 2003 00:00
  • 2. Synthesis and alkylation of some [1,2,4]triazolo[4,3-b]tetrazines

    Synthesis and alkylation of some [1,2,4]triazolo[4,3-b]tetrazines, Zoltán Novák, Antal Csámpai, András Kotschy, Arkivoc 2000, 1, 259-265. (GJ-12EP) | [Full Text Link]

    Two [1,2,4]triazolo[4,3-b]tetrazines were synthesised and alkylated using various reagents. The formation of the ethylated [1,2,4]triazolo[4,3-b]tetrazinium salts and their structure was unambiguously established using correlational NMR spectroscopy. The product distribution was interpreted on the basis of quantum chemical calculations. The triazolotetrazinium salts were found to dealkylate on workup to give the corresponding tetrafluoroborate salts.

    Written on Sunday, 19 November 2000 00:00
  • 1. A novel double 'inverse electron-demand' Diels-Alder reaction of azolyldienamines and tetrazines

    A novel double ‘inverse electron-demand’ Diels-Alder reaction of azolyldienamines and tetrazines, András Kotschy, Zoltán Novák, Zoltán Vincze, David M. Smith, György Hajós, Tetrahedron Lett. 1999, 40, 6313-6316. DOI10.1016/S0040-4039(99)01184-3 |

    Appropriately substituted azolyldienamines were found to undergo double ‘inverse electron-demand’ Diels-Alder reactions with tetrazine derivatives, yielding azolypyridazines and dihydropyridazines as products.

    Written on Friday, 19 November 1999 00:00