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  • 51.
    Niclas, Solin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kjellgren, Johan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Electrophilic Substitution via Monoallylpalladium Intermediates2003In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 42, no 31, p. 3656-3658Article in journal (Refereed)
  • 52.
    Niclas, Solin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sanjay, Narayan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Control of the Regioselectivity in Catalytic Transformations Involving Amphiphilic Bis-allylpalladium Intermediates: Mechanism and Synthetic Applications2001In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 66, no 5, p. 1686-1693Article in journal (Refereed)
    Abstract [en]

    Various dialkyl-substituted allyl chloride derivatives (2d−i) undergo regioselective palladium-catalyzed coupling reactions with allylstannanes (1a,b) and benzylidenemalonitrile (4), providing functionalized 1,7-octadienes in good yield. The catalytic reaction proceeds through an unsymmetrical amphiphilic bis-allylpalladium intermediate. An introductory electrophilic attack on the terminal position of the unsubstituted allyl moiety is followed by a nucleophilic attack on the alkyl-substituted allyl ligand. A theoretical analysis was performed by applying density functional theory at the B3PW91/DZ+P level to study the substituent effects on the electrophilic attack. According to the theoretical results, the high regioselectivity can be ascribed to the electronic effects of the alkyl substituents: The terminal alkyl groups destabilize the η13-bis-allylpalladium intermediate of the reaction; in addition, the alkyl substitution increases the activation barrier for the electrophilic attack.

  • 53.
    Niclas, Solin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanism of the η3-η1-η3 Isomerization in Allylpalladium Complexes: Solvent Coordination, Ligand, and Substituent Effects2001In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 20, p. 5464-5471Article in journal (Refereed)
    Abstract [en]

    The mechanism of the η3 → η1 → η3 isomerization of (η3-allyl)palladium complexes occurring as catalytic intermediates in important synthetic transformations has been studied by applying density functional theory at the B3PW91(DZ+P) level. It was found that under catalytic conditions, in the condensed phase, the isomerization process involves tetracoordinated (η1-allyl)palladium intermediates. In these intermediates a solvent molecule or another ancillary ligand coordinates to palladium. The stability of the (η1-allyl)palladium intermediates critically depends on the electronic effects and on the coordination ability of the solvent molecules and the ancillary ligands. The theoretical calculations indicate a dσ → π* type hyperconjugative interaction occurring in the η1-allyl moiety of the intermediary complexes. These hyperconjugative interactions influence the structure of the complexes and the activation barrier to rotation through the C1−C2 bond. Alkyl substitution of the metalated carbon leads to destabilization of the (η1-allyl)palladium complexes, which increases the activation energy of the syn/anti isomerization process. This substituent effect arises from a dual steric and electronic destabilizing interaction between the methyl substituent and the metal atom.

  • 54.
    Olsson, Vilhelm J.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sebelius, Sara
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selander, Nicklas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium pincer complex catalyzed synthesis and application of allyl boronic acis2007In: Abstracts of Papers, 233rd ACS National Meeting, Chicago, IL, United States, March 25-29, 2007, 2007Conference paper (Other academic)
  • 55.
    Olsson, Vilhelm J.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sebelius, Sara
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Wallner, Olov A.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Employment of functionalized allyl boronic acids in palladium catalyzed regioselective coupling with aryl halides2007In: Abstracts of Papers, 233rd ACS National Meeting, Chicago, IL, United States, March 25-29, 2007, 2007Conference paper (Other academic)
  • 56.
    Olsson, Vilhelm J.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic carbon-hydrogen bond functionalization via in situ generated allyl and vinyl boronates2008In: Abstracts of Papers, 235th ACS National Meeting, New Orleans, LA, United States, April 6-10, 2008, 2008Conference paper (Other academic)
  • 57.
    Olsson, Vilhelm J.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selective one-pot carbon-carbon bond formation by catalytic boronation of unactivated cycloalkenes and subsequent coupling2007In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 46, no 36, p. 6891-6893Article in journal (Refereed)
  • 58.
    Olsson, Vilhelm J.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of allylsilanes and dienylsilanes by a one-pot catalytic C-H borylation-Suzuki-Miyaura coupling sequence2008In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 10, no 14, p. 3129-3131Article in journal (Refereed)
  • 59.
    Pilarski, Lukasz T.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Janson, Pär G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Selective Acyloxylation Using Sodium Perborate as Oxidant2011In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 76, no 5, p. 1503-1506Article in journal (Refereed)
    Abstract [en]

    Sodium perborate (SPB), a principal component of washing powders, was employed as an inexpensive and eco-friendly oxidant in the palladium-catalyzed C-H acyloxylation of alkenes in excellent regio- and stereochemistry. The reactions used anhydrides as acyloxy sources. The method applies to both terminal and internal alkenes, and even benzylic C-H oxidation.

  • 60.
    Pilarski, Lukasz T.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Diphenyliodonium hexafluorophosphate2011In: Encyclopedia of Reagents for Organic Synthesis, John Wiley & Sons, 2011Chapter in book (Refereed)
  • 61.
    Pilarski, Lukasz T.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium Pincer Complex Catalyzed Funtionalization of Electrophiles2011In: Current organic chemistry, ISSN 1385-2728, E-ISSN 1875-5348, Vol. 15, no 18, p. 3389-3414Article in journal (Refereed)
    Abstract [en]

    This review describes the usefulness of palladium pincer complexes in catalytic transformations of various electrophiles. We discuss two basic approaches to the functionalization of electrophiles: (i) palladium pincer complex catalyzed additions of allylic and other substrates to electrophiles, such as sulfonyl imines, aldehydes and related reagents; and (ii) pincer complex catalyzed generation of allylmetal reagents (such as boronates and other species) followed by a direct or palladium-catalyzed functionalization of the electrophiles under one-pot conditions. The study is focused on the reactivity and selectivity aspects of pincer complex catalysis. We show, for example, that allylations of imines and aldehydes are easier to perform with pincer complexes bearing pi-acceptor phosphine ligands, while generation of organometallic species can be efficiently achieved by sigma-donor, selenium or nitrogen containing pincer ligands. We present several examples of chiral pincer complexes in asymmetric catalysis. The high stability and well-defined stoichiometry of pincer-complexes allow a rational design of asymmetric catalytic reactions for carbon-carbon and carbon-heteroatom bond formations. Briefly, we have also reviewed the new emerging field of pincer complexes in Pd(II)/Pd(IV)-based catalytic cycles. These processes allow redox reactions involving pincer complex catalysts without altering of the typical pincer complex topology.

  • 62.
    Sebelius, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olsson, Vilhelm J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Wallner, Olov A.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Coupling of Allylboronic Acids with Iodobenzenes. Selective Formation of the Branched Allylic Product in the Absence of Directing Groups2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 25, p. 8150-8151Article in journal (Refereed)
    Abstract [en]

    Palladium-catalyzed coupling reactions of functionalized allylboronic acids with iodobenzenes were achieved under standard Suzuki−Miyaura coupling conditions. The coupling reactions afforded selectively the branched allylic products in high to excellent yields. In contrast to palladium-catalyzed nucleophilic substitution reactions proceeding via (η3-allyl)palladium intermediates, this process does not require directing groups in the allyl moiety to achieve substitution at the congested allylic terminus. The regioselectivity of the process was largely unaffected by the substituent effects of the iodobenzenes and the allylic substrates.

  • 63.
    Seenivasaperumal, Muthu
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Federsel, Hans-Jürgen
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanism of the asymmetric sulfoxidation in the esomeprazole process: Effects of the imidazole backbone for the enantioselection2009In: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 351, no 6, p. 903-919Article in journal (Refereed)
  • 64.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kipke, Andreas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sebelius, Sara
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Petasis borono-Mannich reaction and allylation of carbonyl compounds via transient allyl boronates generated by palladium-catalyzed substitution of allyl alcohols: An efficient one-pot route to stereodefined alpha-amino acids and homoallyl alcohols2007In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, no 44, p. 13723-13731Article in journal (Refereed)
    Abstract [en]

    An efficient one-pot procedure was designed by integration of the pincer-complex-catalyzed borylation of allyl alcohols in the Petasis borono-Mannich reaction and in allylation of aldehydes and ketones. These procedures are suitable for one-pot synthesis of α-amino acids and homoallyl alcohols from easily available allyl alcohol, amine, aldehyde, or ketone substrates. In the presented transformations, the active allylating agents are in situ generated allyl boronic acid derivatives. These transient intermediates are proved to be reasonably acid-, base-, alcohol-, water-, and air-stable species, which allows a high level of compatibility with the reaction conditions of the allylation of various aldehyde/ketone and imine electrophiles. The boronate source of the reaction is diboronic acid or in situ hydrolyzed diboronate ester ensuring that the waste product of the reaction is nontoxic boric acid. The regio- and stereoselectivity of the reaction is excellent, as almost all products form as single regio- and stereoisomers. The described procedure is suitable to create quaternary carbon centers in branched allylic products without formation of the corresponding linear allylic isomers. Furthermore, products comprising three stereocenters were formed as single products without formation of other diastereomers. Because of the highly disciplined consecutive processes, up to four-step, four-component transformations could be performed selectively as a one-pot sequence. For example, stereodefined pyroglutamic acid could be prepared from a simple allyl alcohol, a commercially available amine, and glyoxylic acid in a one-step procedure. The presented method also grants an easy access to stereodefined 1,7-dienes that are useful substrates for Grubbs ring-closing metathesis.

  • 65.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olsson, Vilhelm J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Scope and mechanism of the palladium pincer complex catalyzed boronation of allyl alcohols2008In: Abstracts of Papers, 235th ACS National Meeting, New Orleans, LA, United States, April 6-10, 2008, 2008Conference paper (Other academic)
  • 66.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Paasch, Jennifer R.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Allylic C-OH Functionalization for Efficient Synthesis of Functionalized Allylsilanes2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 3, p. 409-411Article in journal (Refereed)
    Abstract [en]

    A new method is described for palladium-catalyzed allylic silylation using allylic alcohols and disilanes as precursors. The reactions proceed smoothly under mild and neutral conditions, and this method is suitable for synthesis of regio-and stereodefined allylsilanes. The presented silylation reaction can be easily extended to include synthesis of allylboronates by change of the dimetallic reagent. The presented synthetic procedure offers a broad platform for the selective synthesis of functionalized allyl metal reagents, which are useful precursors in advanced organic chemistry and natural product synthesis.

  • 67.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sebelius, Sara
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Estay, Cesar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Highly Selective and Robust Palladium-Catalysed Carbon-Carbon Coupling between Allyl Alcohols and Aldehydes via Transient Allylboronic Acids2006In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 18, p. 4085-4087Article in journal (Refereed)
    Abstract [en]

    The highly regio- and stereoselective coupling of allyl alcohols with aldehydes could be achieved with 5 mol-% of SeCSe pincer complex catalyst and p-toluenesulfonic acid in the presence of diboronic acid. The transformations have a broad synthetic scope, and the high yields were obtained without the use of an inert atmosphere and carefully dried solvents.

  • 68.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sebelius, Sara
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olsson, Vilhelm J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Allylation of aldehydes by allyl alcohols via palladium pincer complex catalyzed formation of transient allylboronic acids2007In: Abstracts of Papers, 233rd ACS National Meeting, Chicago, IL, United States, March 25-29, 2007, 2007Conference paper (Other academic)
  • 69.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalysis by Palladium Pincer Complexes2011In: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 111, no 3, p. 2048-2076Article, review/survey (Refereed)
  • 70.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Efficient synthesis of α-amino acids via organoboronate reagents2009In: Asymmetric Synthesis and Application of α-Amino Acids / [ed] Vadim A. Soloshonok and Kunisuke Izawa, Washington, DC, USA: American Chemical Society , 2009, p. 190-202Chapter in book (Other academic)
  • 71.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Single-pot triple catalytic transformations based on coupling of in situ generated allyl boronates with in situ hydrolyzed acetals2008In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 29, p. 3420-3422Article in journal (Refereed)
  • 72.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis and transformation of organoboronates and stannanes by pincer-complex catalysts2009In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 32, p. 6267-6279Article in journal (Refereed)
  • 73.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of stereodefined substituted cycloalkenes by a one-pot catalytic boronation-allylation-metathesis sequence2008In: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 350, no 13, p. 2045-2051Article in journal (Refereed)
    Abstract [en]

    Stereodefined cyclohexene and cyclopentene derivatives were prepared by the coupling of allylic alcohols and other allylic precursors with unsaturated aldehydes. These reactions are based on a multicatalytic one-pot approach involving palladium pincer complex-catalyzed boronation, allylation and ring-closing metathesis reactions. This reaction sequence can be performed in an operationally simple procedure affording the cycloalkene products in high overall yields and excellent regio- and stereoselectivities. The presented procedure has a broad synthetic scope and high functional group tolerance, which allows the synthesis of bicyclic lactone and spirane skeletons and various substitution patterns including hydroxy, silyl, vinyl, allyl, and sulfonyl groups. The studied catalytic one-pot reactions involve up to three individual processes performed by up to four acid- and transition metal-catalyzed events.

  • 74.
    Selander, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Willy, Benjamin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selective C-H Borylation of Alkenes by Palladium Pincer Complex Catalyzed Oxidative Functionalization2010In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 49, no 24, p. 4051-4053Article in journal (Refereed)
  • 75.
    Solin, Niclas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kjellgren, Johan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pincer complex catalyzed allylation of aldehyde and imine substrates via nucleophilic η1-allyl palladium intermediates: A new concept for palladium catalyzed allylic substitution reactions2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 22, p. 7026-7033Article in journal (Refereed)
  • 76.
    Solin, Niclas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Narayan, Sanjay
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-catalyzed Tandem Bis-allylation of Isocyanates2001In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 3, no 6, p. 909-912Article in journal (Refereed)
    Abstract [en]

    A tandem bis-allylation of p-toluenesulfonyl isocyanate can be achieved by palladium-catalyzed three-component coupling reaction with allylstannanes and allyl chlorides. A high level of regioselectivity can be obtained by the appropriate choice of the allylic substituents. The reaction mechanism and the regiochemistry of the reaction can be explained by formation of an amphoteric bis-allylpalladium intermediate. This bis-allylpalladium intermediate undergoes an initial electrophilic attack on one of the allyl moieties followed by a nucleophilic attack on the other.

  • 77.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Application of chiral pincer complexes in asymmetric catalysis2009In: Abstracts of Papers, 238th ACS National Meeting, Washington, DC, United States, August 16-20, 2009, American Chemical Society , 2009Conference paper (Other academic)
  • 78.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Iridium catalyzed functionalization of allylic and vinylic C-H bonds2009In: Abstracts of Papers, 238th ACS National Meeting, Washington, DC, United States, August 16-20, 2009, American Chemical Society , 2009Conference paper (Other academic)
  • 79.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis and transformation of allyl and allenyl-metal species using palladium pincer complex catalysis2007In: Abstracts of Papers, 233rd ACS National Meeting, Chicago, IL, United States, March 25-29, 2007, 2007Conference paper (Other academic)
  • 80.
    Wallner, Olov A.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Potassium Trifluoro-2-propenylborate2007In: Encyclopedia of Reagents for Organic Synthesis, Wiley , 2007Chapter in book (Refereed)
  • 81.
    Wang, Dong
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    de Wit, Martin J. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of Densely Substituted Conjugated Dienes by Transition-Metal-Free Reductive Coupling of Allenylboronic Acids and Tosylhydrazones2018In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904Article in journal (Refereed)
    Abstract [en]

    Tosylhydrazones and allenylboronic acids underwent a transition-metal-free reductive coupling reaction. This process is suitable for synthesis of tetra- and pentasubstituted conjugated dienes. The corresponding allenyl-Bpin substrate showed a very poor reactivity. The reaction is suggested to involve coupling of the in situ formed diazo compound and allenylboronic acid. The intermediate formed in this coupling undergoes allenyl migration followed by protodeboronation to furnish a conjugated diene as major product.

  • 82.
    Wang, Dong
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Copper-Catalyzed, Stereoselective Cross-Coupling of Cyclic Allyl Boronic Acids with alpha-Diazoketones2017In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 19, no 7, p. 1622-1625Article in journal (Refereed)
    Abstract [en]

    In this study; we present the synthesis of new, Stereodefined allylboronic adds employed to investigate the stereochemistry of the Cu-catalyzed cross-coupling of allylboronic acids with alpha-diazoketones. According to our results, this reaction proceeds with retention of the relative configurtion of the allylberonic acid substrate. We suggest that the stereoinduction step involves a syn S(E)2'-type transrnetalation of the allylboronic acid substrate with a Cu-carbene species.

  • 83.
    Yang, Yuzhu
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of Allenes by Catalytic Coupling of Propargyl Carbonates with Aryl Iodides in the Presence of Diboron Species2016In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 81, no 1, p. 250-255Article in journal (Refereed)
    Abstract [en]

    Bimetallic copper-/palladium-catalyzed multicomponent reaction of propargyl carbonates, aryl iodides, and diboron species was studied. This procedure can be used for synthesis of di-, tri-, and tetra-substituted allenes. Using diboronic acid, the reaction is supposed to proceed via allenylboronic acid intermediate.

  • 84.
    Yuan, Weiming
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Rhodium-Catalyzed Geminal Oxyfluorination and Oxytrifluoro-Methylation of Diazocarbonyl Compounds2016In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 55, no 29, p. 8410-8415Article in journal (Refereed)
    Abstract [en]

    A new reaction for the rhodium-catalyzed geminal-difunctionalization-based fluorination is presented. The substrates are aromatic and aliphatic diazocarbonyl compounds. As the fluorine source a stable and easily accessible benziodoxole reagent was used. A variety of alcohol, phenol, and carboxylic acid reagents were employed to introduce the second functionality. The reaction was extended to trifluoromethylation using a benziodoxolon reagent. The fluorination and trifluoromethylation reactions probably proceed by a rhodium-containing onium ylide type intermediate, which is trapped by either the F or CF3 electrophiles.

  • 85.
    Zhang, Jiji
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Metathesis Mechanism of Zinc-Catalyzed Fluorination of Alkenes with Hypervalent Fluoroiodine2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 2, p. 1093-1100Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations are used to unravel the mechanism of the Zn-catalyzed fluorocyclization reaction of alkenes using fluoro-benziodoxole reagent. In the initial step Zn coordinates to the fluorine atom of the fluoro-benziodoxole reagent. An important activation step for the fluorination involves Zn-mediated isomerization of the benziodoxole reagent. The activation is followed by a metathesis step to form the C-F bond and a nucleophilic substitution, closing the ring to yield the final aminofluorination product. This mechanism has feasible energy barriers and accounts for the observed selectivity outcome. An alternative mechanism involving an iodocyclopropylium cation intermediate is shown to be associated with high energies.

  • 86.
    Zhao, Jian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jonker, Sybrand J. T.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Meyer, Denise N.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Schulz, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tran, C. Duc
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Copper-catalyzed synthesis of allenylboronic acids. Access to sterically encumbered homopropargylic alcohols and amines by propargylboration2018In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 9, no 13, p. 3305-3312Article in journal (Refereed)
    Abstract [en]

    Tri- and tetrasubstituted allenylboronic acids were prepared via a new versatile copper-catalyzed methodology. The densely functionalized allenylboronic acids readily undergo propargylboration reactions with ketones and imines without any additives. Catalytic asymmetric propargylborylation of ketones is demonstrated with high stereoselectivity allowing for the synthesis of highly enantioenriched tertiary homopropargyl alcohols. The reaction is suitable for kinetic resolution of racemic allenylboronic acids affording alkynes with adjacent quaternary stereocenters.

  • 87.
    Zhao, Jian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic Borylative Opening of Propargyl Cyclopropane, Epoxide, Aziridine, and Oxetane Substrates: Ligand Controlled Synthesis of Allenyl Boronates and Alkenyl Diboronates2016In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 55, no 4, p. 1502-1506Article in journal (Refereed)
    Abstract [en]

    A new copper-catalyzed reaction for the stereo- and regioselective synthesis of alkenyl diboronates and allenyl boronates is presented. In this process propargyl derivatives of strained three/four-membered rings were employed as substrates and B(2)pin(2) was used as the boronate source. Selective formation of the alkenyl diboronate versus the allenyl boronate products was controlled by the choice of phosphine ligand.

  • 88.
    Zhao, Tony S. N.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Trifluoromethylation of Propargylic Halides and Trifluoroacetates Using (Ph3P)(3)Cu(CF3) Reagent2012In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 14, no 15, p. 3966-3969Article in journal (Refereed)
    Abstract [en]

    A copper-mediated trifluoromethylation of propargylic halides and trifluoroacetates was performed with high allenyl or propargyl selectivity. The reaction proceeds smoothly with aliphatic and aromatic substituents bearing either electron-withdrawing or -supplying groups. Preliminary mechanistic results indicate an ionic mechanism involving nucleophilic transfer of the CF3 group from the Cu complex to the propargylic substrate.

  • 89.
    Zhao, Tony S. N.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Yuzhu
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lessing, Timo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Borylation of Propargylic Substrates by Bimetallic Catalysis. Synthesis of Allenyl, Propargylic, and Butadienyl Bpin Derivatives2014In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 136, no 21, p. 7563-7566Article in journal (Refereed)
    Abstract [en]

    Bimetallic Pd/Cu and Pd/Ag catalytic systems were used for borylation of propargylic alcohol derivatives. The substrate scope includes even terminal alkynes. The reactions proceed stererospecifically with formal S(N)2' pathways to give allenyl boronates. Opening of propargyl epoxides leads to 1,2-diborylated butadienes probably via en allenylboronate intermediate.

  • 90.
    Zhao, Tony S. N.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zhao, Jian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stereoselective Synthesis of 1,4-Diols by a Tandem Allylboration–Allenylboration Sequence2015In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 17, no 9, p. 2290-2293Article in journal (Refereed)
    Abstract [en]

    The reaction of mono- and dialdehydes with bis-borodienes (incorporating an allylboronate unit) has been studied. It was found that the initial allylboration reaction results in an allenylboronate, which has two stereogenic units: one of them has axial chirality and the other one is a stereogenic carbon center. This reaction proceeds with high diastereoselectivity. The allenylboronate formed in the allylboration reacts with an additional aldehyde with fair to high stereoselectivity depending on the aldehyde substrate. Aromatic dialdehydes react with bis-boro-butadienes creating three new stereocenters with usually high diastereoselectivity.

12 51 - 90 of 90
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