Boron tribromide as a reagent for anti-Markovnikov addition of HBr to cyclopropanes

Although radical formation from a trialkylborane is well documented, the analogous reaction mode is unknown for trihaloboranes. We have discovered the generation of bromine radicals from boron tribromide and simple proton sources, such as water or tert -butanol, under open-flask conditions. Cyclopro...

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Bibliographic Details
Published in:Chemical science (Cambridge) 2020-08, Vol.11 (35), p.9426-9433
Main Authors: Gieuw, Matthew H, Chen, Shuming, Ke, Zhihai, Houk, K. N, Yeung, Ying-Yeung
Format: Article
Language:English
Subjects:
Boron
Bromination
Bromine
Butanol
Chemistry
Crystallography
NMR
Nuclear magnetic resonance
Organic compounds
Reagents
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Summary:Although radical formation from a trialkylborane is well documented, the analogous reaction mode is unknown for trihaloboranes. We have discovered the generation of bromine radicals from boron tribromide and simple proton sources, such as water or tert -butanol, under open-flask conditions. Cyclopropanes bearing a variety of substituents were hydro- and deuterio-brominated to furnish anti-Markovnikov products in a highly regioselective fashion. NMR mechanistic studies and DFT calculations point to a radical pathway instead of the conventional ionic mechanism expected for BBr 3 . Anti-Markovnikov hydrobromination of cyclopropanes was achieved using boron tribromide and water as the bromine and proton sources, respectively.
ISSN:2041-6520
2041-6539
DOI:10.1039/d0sc02567d