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Alkyl Bromides as Mild Hydride Sources in Ni-Catalyzed Hydroamidation of Alkynes with Isocyanates

  • Wang, Xueqiang
  • Nakajima, Masaki
  • Serrano, Eloisa
  • Martin, Ruben
A catalytic hydroamidation of alkynes with isocyanates using alkyl bromides as hydride sources has been developed. The method turns parasitic β-hydride elimination into a strategic advantage, rapidly affording acrylamides with excellent chemo- and regioselectivity.
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A Mild & Ligand-Free Ni-Catalyzed Silylation via C–OMe Cleavage

  • Zarate, Cayetana
  • Nakajima, Masaki
  • Martin, Ruben
Metal-catalyzed transformations that forge carbon–heteroatom bonds are of central importance in organic synthesis. Despite the formidable potential of aryl methyl ethers as coupling partners, the scarcity of metal-catalyzed C–heteroatom bond formations via C–OMe cleavage is striking, with isolated precedents requiring specialized, yet expensive, ligands, high temperatures, and π-extended backbones. We report an unprecedented catalytic ipso-silylation of aryl methyl ethers under mild conditions and without recourse to external ligands. The method is distinguished by its wide scope, which includes the use of benzyl methyl ethers, vinyl methyl ethers, and unbiased anisole derivatives, thus representing a significant step forward for designing new C–heteroatom bond formations via C–OMe scission. Applications of this transformation in orthogonal silylation techniques as well as in further derivatizations are also described. Preliminary mechanistic experiments suggest the intermediacy of Ni(0)-ate complexes, leaving some doubt that a canonical catalytic cycle consisting of an initial oxidative addition of the C–OMe bond to Ni(0) species comes into play.
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Ni-catalyzed Reductive Carboxylation of Cyclopropyl Motifs with CO2

  • Moragas, Toni
  • Martin, Ruben
A nickel-catalyzed reductive carboxylation technique for the synthesis of cyclopropanecarboxylic acids has been developed. This user-friendly and mild transformation operates at atmospheric pressure of carbon dioxide and utilizes either organic halides or alkene precursors, thus representing the first example of catalytic reductive carboxylation of secondary counterparts lacking adjacent π-components.
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Visible Light-Promoted Atom Transfer Radical Cyclization of Unactivated Alkyl Iodides

  • Shen, Yangyang
  • Cornella, Josep
  • Juliá-Hernández, Francisco
  • Martin
  • Martin, Ruben
A visible-light-mediated atom transfer radical cyclization of unactivated alkyl iodides is described. This protocol operates under mild conditions and exhibits high chemoselectivity profile while avoiding parasitic hydrogen atom transfer pathways. Preliminary mechanistic studies challenge the perception that a canonical photoredox catalytic cycle is being operative.
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Designing Homogeneous Bromine Redox Catalysis for Selective Aliphatic C-H Bond Functionalization

  • Becker, Peter
  • Duhamel, Thomas
  • Martínez, Claudio
  • Muñiz, Kilian
Das Potential der homogenen Oxidationskatalyse unter Verwendung von Brom ist weitgehend unerforscht. Wir zeigen hier, dass die Kombination von Tetraalkylammoniumbromid und 3‐Chlorperbenzoesäure ein einzigartiges Katalysatorsystem für die bequeme und selektive Oxidation gesättigter C(sp3)‐H‐Bindungen unter photochemischer Initiierung mit Tageslicht bietet. Es ermöglicht eine positionsselektive intramolekulare Aminierung, wie anhand von 20 verschiedenen Beispielen gezeigt wurde. Zum ersten Mal konnte ein N‐halogeniertes Intermediat in einer katalytischen Hofmann‐Löffler‐Reaktion isoliert werden. Darüber hinaus wurde eine neuartige schnelle Eintopfsynthese von N‐Sulfonyloxaziridinen aus N‐Sulfonamiden entwickelt und für 15 Transformationen beispielhaft dargestellt. Diese bahnbrechenden Beispiele bieten ein neuartiges Konzept für die molekulare Katalyse mit Brom.
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Catalytic Asymmetric Diamination of Styrenes

  • Muñiz, Kilian
  • Barreiro, Laura
  • Romero, Martín
  • Martínez, Claudio
An enantioselective catalytic vicinal diamination of styrenes is reported, which proceeds under entirely intermolecular reaction control. It relies on a chirally modified aryliodine(I) catalyst and proceeds within an iodine(I/III) manifold with conventional 3-chloroperbenzoic acid as a terminal oxidant. An environmentally benign solvent combination not only adds to the attractiveness of the process but also slows down the rate of the undesired background reaction. A total of 30 examples are presented, which consistently provide high enantiomeric excesses in the range 91–98%.
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Dioxoiodane Compounds as Versatile Sources for Iodine(I) Chemistry

  • Muñiz, Kilian
  • Garcia, Belén
  • Martinez, Claudio
  • Piccinelli, Alessandro
The general synthesis, isolation and characterization of electrophilic iodine reagents of the general formula R4N[I(O2CAr)2] is reported. These compounds are air‐ and moisture‐stable iodine(I) reagents, which were characterized including X‐ray analysis. They represent conceptually new iodine(I) reagents with anions as stabilizers. These compounds display the expected performance as electrophilic reagents upon interaction with electron‐rich substrates. The performance of these compounds in a total of 47 different reactions of vicinal iodooxygenation of alkenes is studied and some key features on the reagents are revealed.
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Dual Intermolecular Allylic C-H Functionalization within the Tetrasubstituted Alkene Scaffold

  • Martínez, Claudio
  • Muñiz, Kilian
Activation of chloramine‐T (TsNNaCl) with a Brønsted acid generates an active reagent for the double allylic C–H functionalization of tetrasubstituted alkenes in an intermolecular manner. The reaction generates a carbon–nitrogen and a carbon–chlorine bond, and proceeds with complete regio‐ and chemoselectivity. A total of 14 examples demonstrate the applicability of the dual C–H functionalization process. The mechanism involves the intermediacy of a 1,3‐butadiene derivative; 1,3‐butadienes can also be used directly as substrates.
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Engineering Molecular Iodine Catalysis for Alkyl- Nitrogen Bond Formation

  • Duhamel, Thomas
  • Stein, Christopher J.
  • Martínez, Claudio
  • Reiher, Markus
  • Muñiz, Kilian
An advanced protocol for the intramolecular C–H amination of alkyl groups via amidyl radicals (Hofmann–Löffler reaction) under homogeneous iodine catalysis is reported. This protocol employs common mCPBA as terminal oxidant. It proceeds under mild conditions, with complete chemoselectivity, is compatible with radical intermediates, and allows for the selective intramolecular amination reaction of secondary and tertiary hydrocarbon bonds and is not restricted to benzylic C–H amination. The involvement of an iodine(III) catalyst state in the C–N bond formation derives from selective oxidation at the stage of the corresponding alkyl iodide with mCPBA. Its formation is corroborated by quantum-chemical calculations. This new catalysis thus proceeds within a defined iodine(I/III) catalysis manifold.
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Organocatalytic Enantioselective Continuous Flow Cyclopropanation

  • Llanes, Patricia
  • Rodríguez-Escrich, Carles
  • Sayalero, Sonia
  • Pericàs, Miquel A.
A set of six solid-supported diarylprolinol catalysts (varying on the anchoring strategy and the type of polymeric support) has been prepared and applied to the enantioselective cyclopropanation reaction. The selected candidate allows implementation of a long flow experiment (48 h) and generates a library of 12 cyclopropanes by sequential flow experiments. The mildness and utility of the method have enabled a telescoped process in which the outstream is directly used in a Wittig flow reaction.
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