32999-09-0Relevant articles and documents
Radical chain monoalkylation of pyridines
Dénès, Fabrice,Jangra, Harish,Meléndez, Camilo,Mulliri, Kleni,Renaud, Philippe,Rieder, Samuel,Zipse, Hendrik
, p. 15362 - 15373 (2021/12/14)
The monoalkylation of N-methoxypyridinium salts with alkyl radicals generated from alkenes (via hydroboration with catecholborane), alkyl iodides (via iodine atom transfer) and xanthates is reported. The reaction proceeds under neutral conditions since no acid is needed to activate the heterocycle and no external oxidant is required. A rate constant for the addition of a primary radical to N-methoxylepidinium >107 M-1 s-1 was experimentally determined. This rate constant is more than one order of magnitude larger than the one measured for the addition of primary alkyl radicals to protonated lepidine demonstrating the remarkable reactivity of methoxypyridinium salts towards radicals. The reaction has been used for the preparation of unique pyridinylated terpenoids and was extended to a three-component carbopyridinylation of electron-rich alkenes including enol esters, enol ethers and enamides.
Light-Mediated Sulfur-Boron Exchange
Panferova, Liubov I.,Dilman, Alexander D.
supporting information, p. 3919 - 3922 (2021/05/29)
Interaction of sulfides bearing a tetrafluoropyridinyl group with bis(catecholato)diboron followed by treatment with pinacol and triethylamine affording pinacol boronic esters is described. The reaction is promoted by an organic photocatalyst (3DPA2FBN) u
A General Approach to Deboronative Radical Chain Reactions with Pinacol Alkylboronic Esters
André-Joyaux, Emy,Kuzovlev, Andrey,Renaud, Philippe,Tappin, Nicholas D. C.
supporting information, p. 13859 - 13864 (2020/06/10)
The generation of carbon-centered radicals from air-sensitive organoboron compounds through nucleohomolytic substitution at boron is a general method to generate non-functionalized and functionalized radicals. Due to their reduced Lewis acidity, alkylboronic pinacol esters are not suitable substrates. We report their in situ conversion into alkylboronic catechol esters by boron-transesterification with a substoichiometric amount of catechol methyl borate combined with an array of radical chain processes. This simple one-pot radical-chain deboronative method enables the conversion of pinacol boronic esters into iodides, bromides, chlorides, and thioethers. The process is also suitable the formation of nitriles and allylated compounds through C?C bond formation using sulfonyl radical traps. The power of combining radical and classical boron chemistry is illustrated with a modular 5-membered ring formation using a combination of three-component coupling and protodeboronative cyclization.
Metal-Free Radical Borylation of Alkyl and Aryl Iodides
Cheng, Ying,Mück-Lichtenfeld, Christian,Studer, Armido
, p. 16832 - 16836 (2018/11/23)
A metal-free radical borylation of alkyl and aryl iodides with bis(catecholato)diboron (B2cat2) as the boron source under mild conditions is introduced. The borylation reaction is operationally easy to conduct and shows high functional group tolerance and broad substrate scope. Radical clock experiments and density functional theory calculations provide insights into the mechanism and rate constants for C-radical borylation with B2cat2 are disclosed.
Homologation Strategy for the Generation of 1-Chloroalkyl Radicals from Organoboranes
Xu, Gong,Lüthy, Monique,Habegger, Jacqueline,Renaud, Philippe
, p. 1506 - 1519 (2016/03/01)
The generation of 1-bromo and 1-chloroalkyl radicals from organoboranes has been investigated. The direct approach involving the hydroboration of halogenated alkenes is impeded by partial dehalogenation taking place during the hydroboration process. An indirect method involving the generation of B-(1-chloroalkyl)catecholborane by homologation of B-alkylcatecholborane with dichloromethyllithium was developed. A reaction sequence involving a hydroboration reaction, a Matteson homologation, and a radical allylation process has been performed as a one-pot process that takes advantage of three different reactivities of organoboron species. Starting from styrene derivatives, it was possible to prepare B-(1-chloro-2-arylpropyl)catecholboranes that are excellent precursors to 1-chloro-2-arylpropyl radicals. A concise approach for the synthesis of an optically active α-methylene-γ-lactone from p-chlorostyrene has been developed on the basis of a two-step sequence involving an enantioselective hydroboration-homologation-cyclization reaction followed by a hydrolysis-lactonization process. (Chemical Equation Presented).
A new mild radical route to 3-substituted maleimides using organoboroles
Birch, Peter,Parsons, Andrew F.,Cross, Paul
experimental part, p. 822 - 824 (2012/03/09)
A new, mild, radical route for the synthesis of 3-substituted maleimides has been developed. This new method incorporates alkene hydroboration, conjugate addition-aminoxylation and TEMPO-H elimination in a one-pot procedure, using cheap, readily available
Mechanism and optimisation of the homoboroproline bifunctional catalytic asymmetric aldol reaction: Lewis acid tuning through in situ esterification
Georgiou, Irene,Whiting, Andrew
, p. 2422 - 2430 (2012/04/17)
The use of homoboroproline as a bifunctional catalyst in the asymmetric aldol reaction has been investigated mechanistically, particularly with respect to tuning the Lewis acidity of boron by in situ esterification with mildly sigma-electron withdrawing diols such as hydrobenzoin and tartrate esters. The stability of simple cyclohexyl and cyclopentyl boronate diol esters shows that the 5-ring boronate esters are more stable, which sheds light on the mode of action of esterified homoboroproline catalyst in the enamine-mediated aldol reaction, which is also studied by NMR. The result is reaction optimisation to provide an efficient aldol reaction and a proposed mechanistic proposal. The Royal Society of Chemistry 2012.
Synthesis of unusual oxime ethers by reaction of tetranitromethane with B-alkylcatecholboranes
Luethy, Monique,Schenk, Kurt,Renaud, Philippe
supporting information; experimental part, p. 10171 - 10177 (2010/12/19)
The reaction of tetranitromethane with B-alkylcatecholboranes leads to the formation of unusual dinitrooxime ethers. A tentative mechanism is provided, which suggests the involvement of extremely fast addition of alkyl radicals to tetranitromethane. The substitution of one of the nitro groups in the oxime ethers by nucleophiles (such as secondary amines, halogens and styrene) and by radicals generated from B-alkylcatecholboranes is reported.
Oxidation of alkylcatecholboranes with functionalized nitroxides for chemical modification of cyclohexene, perallylated polyglycerol and of poly(butadiene)
Wagner, Christine B.,Studer, Armido
experimental part, p. 5782 - 5786 (2011/01/12)
The present communication reports on the synthesis of alkoxyamines by hydroboration of olefins with catecholborane and subsequent oxidation by using nitroxides. Oxidation occurs via a radical process and the intermediately formed C-radicals are trapped by the nitroxides to form the corresponding alkoxyamines. If functionalized nitroxides are used, the method allows incorporation of interesting functional moieties via this approach. The novel method is applied for chemical modification of cyclohexene as a test substrate. More importantly, it is also shown that the reaction sequence can be used for chemical modification of macromolecules containing multiple double bonds. This is documented by successful functionalization of poly(butadiene) and of perallylated polyglycerol. Functionalized poly(butadiene)s can be prepared by a reaction sequence comprising olefin hydroboration and nitroxide induced oxidation to give poly(alkoxyamines). If the nitroxide is charged with aninteresting functional moiety such as a sugar derivative or a polyethylene glycol tail, the trapping process delivers the corresponding functionalized chemically modified poly(olefins) in a one-pot process.
B-alkylcatecholborane-mediated tandem radical conjugated addition-aldol cyclization
Beauseigneur, Alice,Ericsson, Cecilia,Renaud, Philippe,Schenk, Kurt
supporting information; experimental part, p. 3778 - 3781 (2011/02/28)
Image Presented A one-pot procedure involving radical conjugate addition of B-alkylcatecholboranes to enones followed by intramolecular aldol reaction is reported. Application to the stereoselective synthesis of monocyclic and bicyclic products with up to
