Personne : Jayaraman, Arumugam
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Groupe Fontaine, Synthèse Organométallique, Université Laval
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- PublicationAccès libreMetal-free borylation of heteroarenes using ambiphilic aminoboranes : on the importance of sterics in frustrated lewis pair C-H bond activation(American Chemical Society, 2017-10-18) Légaré-Lavergne, Julien; Fontaine, Frédéric-Georges; Misal Castro, Luis Carlos; Rochette, Étienne; Jayaraman, ArumugamTwo novel frustrated Lewis pair (FLP) aminoboranes, (1-Pip-2-BH2-C6H4)2 (2; Pip = piperidyl) and (1-NEt2-2-BH2-C6H4)2 (3; NEt2 = diethylamino), were synthesized, and their structural features were elucidated both in solution and in the solid state. The reactivity of these species for the borylation of heteroarenes was investigated and compared to previously reported (1-TMP-2-BH2-C6H4)2 (1; TMP = tetramethylpiperidyl) and (1-NMe2-2-BH2-C6H4)2 (4; NMe2 = dimethylamino). It was shown that 2 and 3 are more active catalysts for the borylation of heteroarenes than the bulkier analogue 1. Kinetic studies and density functional theory calculations were performed with 1 and 2 to ascertain the influence of the amino group of this FLP-catalyzed transformation. The C–H activation step was found to be more facile with smaller amines at the expense of a more difficult dissociation of the dimeric species. The bench-stable fluoroborate salts of all catalysts (1F–4F) have been synthesized and tested for the borylation reaction. The new precatalysts 2F and 3F are showing higher reaction rates and yields for multigram-scale syntheses.
- PublicationAccès libreRevisiting the reduction of indoles by hydrobranes : a combined experimental and computational study(ScienceDirect, 2019-02-27) Powell-Davies, Henry; Fontaine, Frédéric-Georges; Jayaraman, ArumugamA combined experimental and density functional computational study was used to probe the mechanism for the reduction of indoles using simple borane BH₃·DMS (DMS = dimethyl sulfide). Experimental and computational studies all steer to the formation of the reduced species 1-BH₂-indolines as the resting state for this reaction, as opposed to the historically presumed formation of the unreduced 1-BH₂-indoles, before the addition of a proton source to form the final product indolines. Furthermore, it was observed that molecular H₂ was generated and consumed in the reaction. Computations put forward hydroboration followed by protodeborylation as the very reasonable mechanistic route for the formation of experimentally observed major intermediate 1-BH₂ indolines. For the H₂ consumption in the reaction, computations suggest the frustrated Lewis pair-type heterolytic splitting of H₂ by a bis(3-indolinyl)borane intermediate.
- PublicationAccès librePractical and scalable synthesis of borylated heterocycles using bench-stable precursors of metal-free Lewis pair catalysts(ACS Publications, 2018-10-04) Fontaine, Frédéric-Georges; Misal Castro, Luis Carlos; Jayaraman, ArumugamA practical and scalable metal-free catalytic method for the borylation and borylative dearomatization of heteroarenes has been developed. This synthetic method uses inexpensive and conveniently synthesizable bench-stable precatalysts of the form 1-NHR₂-2-BF₃-C₆H₄, commercially and synthetically accessible heteroarenes as substrates, and pinacolborane as the borylation reagent. The preparation of several borylated heterocycles on 2 and 50 g scales was achieved under solvent-free conditions without the use of Schlenk techniques or a glovebox. A kilogram-scale borylation of one of the heteroarene substrates was also achieved using this cost-effective green methodology to exemplify the fact that our methodology can be conveniently implemented in fine chemical industries.
- PublicationAccès libreMetal-free borylative dearomatization of indoles : exploring the divergent reactivity of aminoborane C–H borylation catalysts(Royal Society of Chemistry, 2018-05-07) Fontaine, Frédéric-Georges; Misal Castro, Luis Carlos; Jayaraman, Arumugam; Desrosiers, VincentWhile the dearomatization of indoles by carbon–boron bond forming reactions is new and quite promising, they are so far mainly metal-catalyzed. Here, we establish the use of metal-free catalysts in promoting such reactions in an atom-efficient way. The in situ generated ambiphilic aminoborane catalyst (1-Pip-2-BH2-C6H4)2 (Pip = piperidyl) promotes borylative dearomatization of various 1-arylsulfonyl indoles with pinacolborane in a syn addition fashion, with H and Bpin groups added respectively to the 2 and 3 positions of indoles. Catalysis proceeds with good to excellent conversion and essentially with complete regio- and diastereoselectivity. From mechanistic insights and DFT computations, we realized and established that prototypical boranes can also catalyze this borylative dearomatization.