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Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors
The one-pot condensation of glyoxal, two equivalents of cyclohexylamine, and paraformaldehyde in the presence of aqueous HBF(4) provided a straightforward access to 1,3-dicyclohexylimidazolium tetrafluoroborate (ICy·HBF(4)). 1,3-Dibenzylimidazolium tetrafluoroborate (IBn·HBF(4)) was obtained along t...
Autores principales: | , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
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Beilstein-Institut
2015
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685873/ https://www.ncbi.nlm.nih.gov/pubmed/26734080 http://dx.doi.org/10.3762/bjoc.11.252 |
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author | Hans, Morgan Lorkowski, Jan Demonceau, Albert Delaude, Lionel |
author_facet | Hans, Morgan Lorkowski, Jan Demonceau, Albert Delaude, Lionel |
author_sort | Hans, Morgan |
collection | PubMed |
description | The one-pot condensation of glyoxal, two equivalents of cyclohexylamine, and paraformaldehyde in the presence of aqueous HBF(4) provided a straightforward access to 1,3-dicyclohexylimidazolium tetrafluoroborate (ICy·HBF(4)). 1,3-Dibenzylimidazolium tetrafluoroborate (IBn·HBF(4)) was obtained along the same lines. To synthesize 1,3-diarylmidazolium salts, it was necessary to isolate the intermediate N,N'-diarylethylenediimines prior to their cyclization. Although this additional step required more time and reagents, it led to a much more efficient overall process. It also proved very convenient to carry out the synthesis of imidazolinium salts in parallel to their imidazolium counterparts via the reduction of the diimines into diammonium salts. The critical assembly of the C(2) precarbenic unit was best achieved with paraformaldehyde and chlorotrimethylsilane in the case of imidazolium derivatives, whereas the use of triethyl orthoformate under microwave irradiation was most appropriate for the fast and efficient synthesis of imidazolinium salts. This strategy was applied to the synthesis of six common N-heterocyclic carbene precursors, namely, 1,3-dimesitylimidazolium chloride (IMes·HCl), 1,3-dimesitylimidazolium tetrafluoroborate (IMes·HBF(4)), 1,3-dimesitylimidazolinium chloride (SIMes·HCl), 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (IDip·HCl or IPr·HCl), 1,3-bis(2,6-diisopropylphenyl)imidazolinium chloride (SIDip·HCl or SIPr·HCl), and 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazolium chloride (IDip*·HCl or IPr*·HCl). |
format | Online Article Text |
id | pubmed-4685873 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2015 |
publisher | Beilstein-Institut |
record_format | MEDLINE/PubMed |
spelling | pubmed-46858732016-01-05 Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors Hans, Morgan Lorkowski, Jan Demonceau, Albert Delaude, Lionel Beilstein J Org Chem Full Research Paper The one-pot condensation of glyoxal, two equivalents of cyclohexylamine, and paraformaldehyde in the presence of aqueous HBF(4) provided a straightforward access to 1,3-dicyclohexylimidazolium tetrafluoroborate (ICy·HBF(4)). 1,3-Dibenzylimidazolium tetrafluoroborate (IBn·HBF(4)) was obtained along the same lines. To synthesize 1,3-diarylmidazolium salts, it was necessary to isolate the intermediate N,N'-diarylethylenediimines prior to their cyclization. Although this additional step required more time and reagents, it led to a much more efficient overall process. It also proved very convenient to carry out the synthesis of imidazolinium salts in parallel to their imidazolium counterparts via the reduction of the diimines into diammonium salts. The critical assembly of the C(2) precarbenic unit was best achieved with paraformaldehyde and chlorotrimethylsilane in the case of imidazolium derivatives, whereas the use of triethyl orthoformate under microwave irradiation was most appropriate for the fast and efficient synthesis of imidazolinium salts. This strategy was applied to the synthesis of six common N-heterocyclic carbene precursors, namely, 1,3-dimesitylimidazolium chloride (IMes·HCl), 1,3-dimesitylimidazolium tetrafluoroborate (IMes·HBF(4)), 1,3-dimesitylimidazolinium chloride (SIMes·HCl), 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (IDip·HCl or IPr·HCl), 1,3-bis(2,6-diisopropylphenyl)imidazolinium chloride (SIDip·HCl or SIPr·HCl), and 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazolium chloride (IDip*·HCl or IPr*·HCl). Beilstein-Institut 2015-11-25 /pmc/articles/PMC4685873/ /pubmed/26734080 http://dx.doi.org/10.3762/bjoc.11.252 Text en Copyright © 2015, Hans et al. https://creativecommons.org/licenses/by/2.0https://www.beilstein-journals.org/bjoc/termsThis is an Open Access article under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The license is subject to the Beilstein Journal of Organic Chemistry terms and conditions: (https://www.beilstein-journals.org/bjoc/terms) |
spellingShingle | Full Research Paper Hans, Morgan Lorkowski, Jan Demonceau, Albert Delaude, Lionel Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors |
title | Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors |
title_full | Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors |
title_fullStr | Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors |
title_full_unstemmed | Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors |
title_short | Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors |
title_sort | efficient synthetic protocols for the preparation of common n-heterocyclic carbene precursors |
topic | Full Research Paper |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685873/ https://www.ncbi.nlm.nih.gov/pubmed/26734080 http://dx.doi.org/10.3762/bjoc.11.252 |
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