LiTMP trans-metal-trapping of fluorinated aromatic molecules: a comparative study of Al and Ga carbanion traps

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Abstract

Fluoro aromatic scaffolds pose a challenge to lithiation due to low stability of lithiated intermediates. Here we apply trans-metal-trapping (TMT) to a series of key fluorinated aromatics. In TMT, LiTMP performs the metallation, while an organometallic trap intercepts the emergent carbanion. This study contrasts the trapping abilities of iBu2AlTMP and Ga(CH2SiMe3)3, structurally mapping their TMT reactions and probing relative stabilities of metallated fluoroaromatic intermediates by NMR studies. Results show the installed Al-C(aryl) bonds are more prone to decomposition by benzyne formation and Li-F liberation, than the Ga-C(aryl) species. The latter are thus better for onward reactivity as demonstrated in cross-coupling reactions with benzoyl chloride that produce ketones.
LanguageEnglish
Pages9566-9570
Number of pages5
JournalAngewandte Chemie International Edition
Volume56
Issue number32
Early online date17 Jul 2017
DOIs
Publication statusPublished - 1 Aug 2017

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Metals
Molecules
Cross Reactions
Organometallics
Ketones
Scaffolds
Nuclear magnetic resonance
Decomposition
benzoyl chloride
benzyne

Keywords

  • aluminium
  • carbanions
  • fluoroaromatic compounds
  • gallium
  • metallation
  • structure elucidation

Cite this

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title = "LiTMP trans-metal-trapping of fluorinated aromatic molecules: a comparative study of Al and Ga carbanion traps",
abstract = "Fluoro aromatic scaffolds pose a challenge to lithiation due to low stability of lithiated intermediates. Here we apply trans-metal-trapping (TMT) to a series of key fluorinated aromatics. In TMT, LiTMP performs the metallation, while an organometallic trap intercepts the emergent carbanion. This study contrasts the trapping abilities of iBu2AlTMP and Ga(CH2SiMe3)3, structurally mapping their TMT reactions and probing relative stabilities of metallated fluoroaromatic intermediates by NMR studies. Results show the installed Al-C(aryl) bonds are more prone to decomposition by benzyne formation and Li-F liberation, than the Ga-C(aryl) species. The latter are thus better for onward reactivity as demonstrated in cross-coupling reactions with benzoyl chloride that produce ketones.",
keywords = "aluminium, carbanions, fluoroaromatic compounds, gallium, metallation, structure elucidation",
author = "Ross McLellan and Marina Uzelac and Kennedy, {Alan R.} and Eva Hevia and Mulvey, {Robert E.}",
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AU - McLellan, Ross

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AU - Hevia, Eva

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AB - Fluoro aromatic scaffolds pose a challenge to lithiation due to low stability of lithiated intermediates. Here we apply trans-metal-trapping (TMT) to a series of key fluorinated aromatics. In TMT, LiTMP performs the metallation, while an organometallic trap intercepts the emergent carbanion. This study contrasts the trapping abilities of iBu2AlTMP and Ga(CH2SiMe3)3, structurally mapping their TMT reactions and probing relative stabilities of metallated fluoroaromatic intermediates by NMR studies. Results show the installed Al-C(aryl) bonds are more prone to decomposition by benzyne formation and Li-F liberation, than the Ga-C(aryl) species. The latter are thus better for onward reactivity as demonstrated in cross-coupling reactions with benzoyl chloride that produce ketones.

KW - aluminium

KW - carbanions

KW - fluoroaromatic compounds

KW - gallium

KW - metallation

KW - structure elucidation

UR - http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1521-3773

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