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syn-1,2-Carboboration of Alkynes with Borenium Cations

The reaction of 8-(trimethylsiloxy)quinoline (QOTMS) with BCl(3) and (aryl)BCl(2) forms QOBCl(2) and QOBCl(aryl). The subsequent addition of stoichiometric AlCl(3) follows one of two paths, dependent on the steric demands of the QO ligand and the electrophilicity of the resulting borenium cation. Th...

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Autores principales: Cade, Ian A, Ingleson, Michael J
Formato: Online Artículo Texto
Lenguaje:English
Publicado: WILEY-VCH Verlag 2014
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4209141/
https://www.ncbi.nlm.nih.gov/pubmed/25138585
http://dx.doi.org/10.1002/chem.201403614
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author Cade, Ian A
Ingleson, Michael J
author_facet Cade, Ian A
Ingleson, Michael J
author_sort Cade, Ian A
collection PubMed
description The reaction of 8-(trimethylsiloxy)quinoline (QOTMS) with BCl(3) and (aryl)BCl(2) forms QOBCl(2) and QOBCl(aryl). The subsequent addition of stoichiometric AlCl(3) follows one of two paths, dependent on the steric demands of the QO ligand and the electrophilicity of the resulting borenium cation. The phenyl- and 5-hexylthienylborenium cations, QOBPh(+) and QOBTh(+), are formed, whereas QOBCl(+) is not. Instead, AlCl(3) preferentially binds with QOBCl(2) at oxygen, forming QOBCl(2)⋅AlCl(3), rather than abstracting chloride. A modest increase in the steric demands around oxygen, by installing a methyl group at the 7-position of the quinolato ligand, switches the reactivity with AlCl(3) back to chloride abstraction, allowing formation of [Image: see text]QOBCl(+). All the prepared borenium cations are highly chlorophilic and exhibit significant interaction with AlCl(4)(−) resulting in an equilibrium concentration of Lewis acidic “AlCl(3)” species. The presence of “AlCl(3)(”) species limits the alkyne substrates compatible with these borenium systems, with reaction of [QOBPh][AlCl(4)] with 1-pentyne exclusively yielding the cyclotrimerised product, 1,3,5-tripropylbenzene. In contrast, QOBPh(+) and QOBTh(+) systems effect the syn-1,2-carboboration of 3-hexyne. DFT calculations at the M06-2X/6-311G(d,p)/PCM(DCM) level confirm that the higher migratory aptitude of Ph versus Me leads to a lower barrier to 1,2-carboboration relative to 1,1-carboboration.
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spelling pubmed-42091412014-11-14 syn-1,2-Carboboration of Alkynes with Borenium Cations Cade, Ian A Ingleson, Michael J Chemistry Full Papers The reaction of 8-(trimethylsiloxy)quinoline (QOTMS) with BCl(3) and (aryl)BCl(2) forms QOBCl(2) and QOBCl(aryl). The subsequent addition of stoichiometric AlCl(3) follows one of two paths, dependent on the steric demands of the QO ligand and the electrophilicity of the resulting borenium cation. The phenyl- and 5-hexylthienylborenium cations, QOBPh(+) and QOBTh(+), are formed, whereas QOBCl(+) is not. Instead, AlCl(3) preferentially binds with QOBCl(2) at oxygen, forming QOBCl(2)⋅AlCl(3), rather than abstracting chloride. A modest increase in the steric demands around oxygen, by installing a methyl group at the 7-position of the quinolato ligand, switches the reactivity with AlCl(3) back to chloride abstraction, allowing formation of [Image: see text]QOBCl(+). All the prepared borenium cations are highly chlorophilic and exhibit significant interaction with AlCl(4)(−) resulting in an equilibrium concentration of Lewis acidic “AlCl(3)” species. The presence of “AlCl(3)(”) species limits the alkyne substrates compatible with these borenium systems, with reaction of [QOBPh][AlCl(4)] with 1-pentyne exclusively yielding the cyclotrimerised product, 1,3,5-tripropylbenzene. In contrast, QOBPh(+) and QOBTh(+) systems effect the syn-1,2-carboboration of 3-hexyne. DFT calculations at the M06-2X/6-311G(d,p)/PCM(DCM) level confirm that the higher migratory aptitude of Ph versus Me leads to a lower barrier to 1,2-carboboration relative to 1,1-carboboration. WILEY-VCH Verlag 2014-09-26 2014-08-19 /pmc/articles/PMC4209141/ /pubmed/25138585 http://dx.doi.org/10.1002/chem.201403614 Text en © 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. http://creativecommons.org/licenses/by-nc/3.0/ This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
spellingShingle Full Papers
Cade, Ian A
Ingleson, Michael J
syn-1,2-Carboboration of Alkynes with Borenium Cations
title syn-1,2-Carboboration of Alkynes with Borenium Cations
title_full syn-1,2-Carboboration of Alkynes with Borenium Cations
title_fullStr syn-1,2-Carboboration of Alkynes with Borenium Cations
title_full_unstemmed syn-1,2-Carboboration of Alkynes with Borenium Cations
title_short syn-1,2-Carboboration of Alkynes with Borenium Cations
title_sort syn-1,2-carboboration of alkynes with borenium cations
topic Full Papers
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4209141/
https://www.ncbi.nlm.nih.gov/pubmed/25138585
http://dx.doi.org/10.1002/chem.201403614
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