402-31-3Relevant articles and documents
A new method of introducing a trifluoromethyl group into an aromatic ring
Zupan, Marko,Bregar, Zvonko
, p. 3357 - 3358 (1990)
Trifluoromethyl derivatives of aromatic molecules were prepared from aromatic halides, converted to dithiocarboxylic acids through formation of Grignard reagents, followed by fluorination with xenon difluoride at room temperature.
Photoredox catalysis on unactivated substrates with strongly reducing iridium photosensitizers
Shon, Jong-Hwa,Kim, Dooyoung,Rathnayake, Manjula D.,Sittel, Steven,Weaver, Jimmie,Teets, Thomas S.
, p. 4069 - 4078 (2021/04/06)
Photoredox catalysis has emerged as a powerful strategy in synthetic organic chemistry, but substrates that are difficult to reduce either require complex reaction conditions or are not amenable at all to photoredox transformations. In this work, we show that strong bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ancillary ligands enable high-yielding photoredox transformations of challenging substrates with very simple reaction conditions that require only a single sacrificial reagent. Using blue or green visible-light activation we demonstrate a variety of reactions, which include hydrodehalogenation, cyclization, intramolecular radical addition, and prenylationviaradical-mediated pathways, with optimized conditions that only require the photocatalyst and a sacrificial reductant/hydrogen atom donor. Many of these reactions involve organobromide and organochloride substrates which in the past have had limited utility in photoredox catalysis. This work paves the way for the continued expansion of the substrate scope in photoredox catalysis.
Cross-Coupling through Ag(I)/Ag(III) Redox Manifold
Demonti, Luca,Mézailles, Nicolas,Nebra, Noel,Saffon-Merceron, Nathalie
supporting information, p. 15396 - 15405 (2021/10/12)
In ample variety of transformations, the presence of silver as an additive or co-catalyst is believed to be innocuous for the efficiency of the operating metal catalyst. Even though Ag additives are required often as coupling partners, oxidants or halide scavengers, its role as a catalytically competent species is widely neglected in cross-coupling reactions. Most likely, this is due to the erroneously assumed incapacity of Ag to undergo 2e? redox steps. Definite proof is herein provided for the required elementary steps to accomplish the oxidative trifluoromethylation of arenes through AgI/AgIII redox catalysis (i. e. CEL coupling), namely: i) easy AgI/AgIII 2e? oxidation mediated by air; ii) bpy/phen ligation to AgIII; iii) boron-to-AgIII aryl transfer; and iv) ulterior reductive elimination of benzotrifluorides from an [aryl-AgIII-CF3] fragment. More precisely, an ultimate entry and full characterization of organosilver(III) compounds [K]+[AgIII(CF3)4]? (K-1), [(bpy)AgIII(CF3)3] (2) and [(phen)AgIII(CF3)3] (3), is described. The utility of 3 in cross-coupling has been showcased unambiguously, and a large variety of arylboron compounds was trifluoromethylated via [AgIII(aryl)(CF3)3]? intermediates. This work breaks with old stereotypes and misconceptions regarding the inability of Ag to undergo cross-coupling by itself.
An Efficient Deprotection of 2,6-Bis(trifluoromethyl)phenylboronic Esters via Catalytic Protodeboronation Using Tetrabutyl ammonium Fluoride
Makino, Kazuishi,Nojima, Shinya,Shimada, Naoyuki,Urata, Sari
supporting information, p. 2300 - 2304 (2019/12/11)
We herein describe an efficient deprotection of 2,6-bis(trifluoromethyl)phenylboronic esters, which serve as effective protective groups for 1,2- or 1,3-diols in various organic transformations, via protodeboronation by using a catalytic amount of tetrabutylammonium fluoride (TBAF).
Synthesis and Characterization of Strong Cyclometalated Iridium Photoreductants for Application in Photocatalytic Aryl Bromide Hydrodebromination
Shon, Jong-Hwa,Sittel, Steven,Teets, Thomas S.
, p. 8646 - 8658 (2019/09/12)
A series of potent bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ancillary ligands is described. Structure-property analysis reveals that substituent modification of the NacNac ligands has a large effect on the ground-state IrIV/IrIII potential, which shifts cathodically as the NacNac is made more electron-rich. In addition, the excited-state IrIV/?IrIII potentials are ca. 300-500 mV more negative than that of fac-Ir(ppy)3 (ppy = 2-phenylpyridine), indicating that these compounds have much more reducing excited states. Rate constants for excited-state electron transfer between these photosensitizers and benzophenone are -2-3 times faster than fac-Ir(ppy)3, demonstrating that these complexes are both kinetically and thermodynamically more potent for excited-state electron transfer. We use these photosensitizers to optimize a simple reaction procedure for photocatalytic debromination of aryl bromide substrates, which requires only the photosensitizer, blue light, and an amine base, without silanes or other additives that are used in previously reported methods.
Palladium-mediated radical homocoupling reactions: A surface catalytic insight
Favier, Isabelle,Toro, Marie-Lou,Lecante, Pierre,Pla, Daniel,Gómez, Montserrat
, p. 4766 - 4773 (2018/09/29)
In this contribution, we report a palladium nanoparticle-promoted reductive homocoupling of haloarenes that proceeds efficiently to produce corresponding bis-aryls in moderate to excellent yields using relatively low catalyst loading (1 mol%), and exhibits broad functional group tolerance. This work sheds light on how the surface state of Pd(0) nanoparticles plays a crucial role in the reactivity of catalytic systems. Notably, the appropriate choice of palladium salts for the preparation of the preformed nanocatalysts was a key parameter having a major impact on the catalytic activity; thus, the effect of halide anions on the reactivity of the as-prepared palladium nanoparticles could be assessed, with iodide anions being capable of inhibiting the corresponding homocoupling reaction. The homocoupling reaction mechanism has been further studied by means of radical trap and electron paramagnetic resonance (EPR) experiments, revealing that the reaction proceeds via radical intermediates. Taking into account these data, a plausible reaction mechanism based on single-electron transfer processes on the palladium nanoparticle surface is discussed.
Visible-Light photoredox decarboxylation of perfluoroarene iodine(III) Trifluoroacetates for C-H trifluoromethylation of (Hetero)arenes
Yang, Bin,Yu, Donghai,Xu, Xiu-Hua,Qing, Feng-Ling
, p. 2839 - 2843 (2018/04/14)
A scalable and operationally simple decarboxylative trifluoromethylation of (hetero)arenes with easily accessible C6F5I(OCOCF3)2 under photoredox catalysis has been developed. This method is tolerant of various (hetero)arenes and functional groups. Notably, C6F5I is recycled from the decarboxylation reaction and further used for the preparation of C6F5I(OCOCF3)2. The combination of photoredox catalysis and hypervalent iodine reagent provides a practical approach for the application of trifluoroacetic acid in trifluoromethylation reactions.
Catalytic Reduction of Alkyl and Aryl Bromides Using Propan-2-ol
Haibach, Michael C.,Stoltz, Brian M.,Grubbs, Robert H.
supporting information, p. 15123 - 15126 (2017/11/20)
Milstein's complex, (PNN)RuHCl(CO), catalyzes the efficient reduction of aryl and alkyl halides under relatively mild conditions by using propan-2-ol and a base. Sterically hindered tertiary and neopentyl substrates are reduced efficiently, as well as more functionalized aryl and alkyl bromides. The reduction process is proposed to occur by radical abstraction/hydrodehalogenation steps at ruthenium. Our research represents a safer and more sustainable alternative to typical silane, lithium aluminium hydride, and tin-based conditions for these reductions.
Base-Catalyzed Aryl-B(OH)2 Protodeboronation Revisited: From Concerted Proton Transfer to Liberation of a Transient Aryl Anion
Cox, Paul A.,Reid, Marc,Leach, Andrew G.,Campbell, Andrew D.,King, Edward J.,Lloyd-Jones, Guy C.
supporting information, p. 13156 - 13165 (2017/09/26)
Pioneering studies by Kuivila, published more than 50 years ago, suggested ipso protonation of the boronate as the mechanism for base-catalyzed protodeboronation of arylboronic acids. However, the study was limited to UV spectrophotometric analysis under acidic conditions, and the aqueous association constants (Ka) were estimated. By means of NMR, stopped-flow IR, and quenched-flow techniques, the kinetics of base-catalyzed protodeboronation of 30 different arylboronic acids has now been determined at pH > 13 in aqueous dioxane at 70 °C. Included in the study are all 20 isomers of C6HnF(5-n)B(OH)2 with half-lives spanning 9 orders of magnitude: a and Sδ values, kinetic isotope effects (2H, 10B, 13C), linear free-energy relationships, and density functional theory calculations, we have identified a mechanistic regime involving unimolecular heterolysis of the boronate competing with concerted ipso protonation/C-B cleavage. The relative Lewis acidities of arylboronic acids do not correlate with their protodeboronation rates, especially when ortho substituents are present. Notably, 3,5-dinitrophenylboronic acid is orders of magnitude more stable than tetra-and pentafluorophenylboronic acids but has a similar pKa.
Aryl(triethyl)silanes for Biaryl and Teraryl Synthesis by Copper(II)-Catalyzed Cross-Coupling Reaction
Komiyama, Takeshi,Minami, Yasunori,Hiyama, Tamejiro
supporting information, p. 15787 - 15791 (2016/12/16)
Aryl(triethyl)silanes are found to undergo cross-coupling with iodoarenes in the presence of catalytic amounts of CuBr2and Ph-Davephos, as well as cesium fluoride as a stoichiometric base. Because the silicon reagents are readily accessible through catalytic C?H silylation of aromatic substrates, the net transformation allows coupling of aromatic hydrocarbons with iodoarenes via triethylsilylation.
