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Radical-chain reductive alkylation of electron-rich alkenes mediated by silanes in the presence of thiols as polarity-reversal catalysts

Lookup NU author(s): Dr Mark Elsegood


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In the presence of a thiol catalyst, triphenylsilane mediates the reductive alkyiation of electron-rich terminal alkenes R'R2C=CH2 by organic halides R3Hal via electrophilic carbon-centred radicals R3'. Reactions were carried out in benzene or dioxane solvent using di-re/7-butyl hyponitrite (at 60 °C) or dilauroyl peroxide (at 80 CC) as initiators and good yields of the adducts R'R2CHCH2R3 were obtained with either methyl thioglycolate or triphenylsilanethiol as catalysts (5-10 mol% based on alkene). In the presence of the thiol, the slow direct abstraction of hydrogen from the silane by the nucleophilic adduct radical R'RCHjR3 is replaced by a cycle of more rapid polarity-matched reactions in which hydrogen-atom transfer to the adduct radical from the thiol is followed by abstraction of hydrogen from the silane by the derived thiyl radical, to regenerate the catalyst. In the absence of thiol, negligible yields of reductive alkyiation products were obtained. The homochiral thiols, 1-thio-p-D-mannopyranose tetraacetate and 1-thioD-glucopyranose tetraacetate, and the tetrapivalate and tetrabenzoate analogues of the latter were effective catalysts and reductive carboxyalkylation products with enantiomeric excesses up to 72% were obtained from prochiral alkenes. Homochiral samples of two of these adducts were obtained by recrystallisation and their absolute configurations were determined by X-ray diffraction.

Publication metadata

Author(s): Dang H-S, Elsegood MRJ, Kirn K-M, Roberts BP

Publication type: Article

Publication status: Published

Journal: Journal of the Chemical Society - Perkin Transactions 1

Year: 1999

Issue: 15

Pages: 2061-2068

Print publication date: 01/01/1999

ISSN (print): 0300-922X

ISSN (electronic): 1364-5463

Publisher: Royal Society of Chemistry


DOI: 10.1039/a903961i


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