An Efficient Radical Procedure for the Halogenation and Chalcogenation of <i>B</i>‐Alkylcatecholboranes

Schaffner, Arnaud‐Pierre; Montermini, Florian; Pozzi, Davide; Darmency, Vincent; Scanlan, Eoin M.; Renaud, Philippe

doi:10.1002/adsc.200700531

Cited by 33 publications

(20 citation statements)

References 52 publications

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“…[8] Desired organoboranes 8-12 are generated in a one-pot process involving hydroboration of α-pinene (1a) with a borane-dimethyl sulfide complex (1 equiv.) followed by reaction with modified catechols 3-7.…”

Section: Resultsmentioning

confidence: 99%

ModifiedB‐Alkylcatecholboranes as Radical Precursors

2010

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Generation of radicals from B-alkylcatecholboranes represents an efficient tin-free procedure for the generation of alkyl radicals. A modified version of this method has been developed. The simple catechol is replaced by a dihydroxylated tetrahydroisoquinoline, which can be separated from the reaction products by simple extraction with an aqueous acid solution. The modified alkyl radical precursors are easily prepared from alkenes by hydroboration with BH 3 ·Me 2 S fol-

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Section: Resultsmentioning

confidence: 99%

ModifiedB‐Alkylcatecholboranes as Radical Precursors

2010

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“…[22,23] The addition of nucleophilic carbon-centered radicals to PhSO 2 SPh is known to result in the formation of thioethers. [24] The presence of other sulfurizing agents (denoted Y-SPh in Scheme 7), however, cannot be ruled out at this stage. In both cases, there was no evidence of products produced by the direct addition of the carbon-centered radical derived from 4 to oxime 9.…”

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Silylboranes as New Sources of Silyl Radicals for Chain‐Transfer Reactions

Rouquet

Robert

Méreau

et al. 2011

Chemistry A European J

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Various silylboranes, which were outfitted with a catecholborane moiety at one end and a (Me(3)Si)(3)Si moiety at the other end of a carbon chain, were prepared through the hydroboration of the corresponding unsaturated silanes. The C-centered radical species generated from these silylboranes efficiently cyclized to provide, through a 5-exo intramolecular homolytic substitution at the silicon center, the corresponding silacycle and a Me(3)Si radical that was subsequently trapped by sulfonyl acceptors. These cyclizations proceeded at unprecedented rates, due, in part, to a strong gem-dialkyl effect that was attributable to the presence of bulky substituents on a quaternary center located on the chain. In parallel, we designed arylsilylboranes that produced silyl radicals through a 1,5-hydrogen transfer. Such silyl radicals may be valuable radical chain carriers, for instance, in oximation reactions of alkyl halides. Finally, computational studies allowed calculation of activation barriers of the homolytic substitution step and additionally illustrated that the overall reaction mechanism involved a transition state in which the attacking carbon center, the central silicon atom, and the Me(3)Si leaving group were collinear.

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“…The reaction was allowed to react for 20 h at room temperature and afforded the desired cyclohexyl phenyl sulfide 8a. 24 The reaction was presumably initiated by traces of oxygen present in the solvent. Addition of a radical initiator like di-tert-butylhyponitrite did not change significantly the reaction outcome.…”

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“…The chlorination reaction with benzenesulfonyl chloride 24 afforded 9b in 94% yield (Scheme 7, eq. 3).…”

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“…This hypothesis is nicely supported by the report of Chung who patented the use of 9-octylperoxy-9-borafluorene, generated by reaction of 9-octyl-9-borafluorene with oxygen, as an initiator for radical living polymerization processes. 22 In connection with our interest in organoboranes and their use as radical precursors, 5,23,24 we decided to synthesize and investigate the use of 9-alkyl-9-borafluorenes in radical reactions. We report herein that these compounds readily afford alkyl radicals that can be trapped successfully.…”

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Radical chain reactions involving 9-alkyl-9-borafluorenes

Gorokhovik¹,

Rieder²,

Povie³

et al. 2014

Arkivoc

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The preparation of 9-alkyl-9-borafluorenes and their use as radical precursors in chain reactions were investigated. These organoboranes were found to be excellent precursors of primary and secondary alkyl radicals. Reactions were readily initiated by traces of oxygen and efficient processes involving sulfonyl-based radical traps were discovered. Due to the very high reactivity of the intermediate 9-H and 9-alkyl-9-borafluorenes, problems of reproducibility were identified.

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An Efficient Radical Procedure for the Halogenation and Chalcogenation of B‐Alkylcatecholboranes

Cited by 33 publications

References 52 publications

ModifiedB‐Alkylcatecholboranes as Radical Precursors

ModifiedB‐Alkylcatecholboranes as Radical Precursors

Silylboranes as New Sources of Silyl Radicals for Chain‐Transfer Reactions

Radical chain reactions involving 9-alkyl-9-borafluorenes

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