Article (Scientific journals)
Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors
Hans, Morgan; Lorkowski, Jan; Demonceau, Albert et al.
2015In Beilstein Journal of Organic Chemistry, 11, p. 2318-2325
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Keywords :
cyclization; experimental procedure; imidazolinium salt; imidazolium salt; microwave heating
Abstract :
[en] The one-pot condensation of glyoxal, two equivalents of cyclohexylamine, and paraformaldehyde in the presence of aqueous HBF4 provided a straightforward access to 1,3-dicyclohexylimidazolium tetrafluoroborate (ICy·HBF4). 1,3-Dibenzylimidazolium tetrafluoroborate (IBn·HBF4) 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 C2 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·HBF4), 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).
Disciplines :
Chemistry
Author, co-author :
Hans, Morgan ;  Université de Liège > Département des sciences de la vie > Centre d'ingénierie des protéines
Lorkowski, Jan
Demonceau, Albert ;  Université de Liège > Département de chimie (sciences) > Chimie macromoléculaire et catalyse organique
Delaude, Lionel  ;  Université de Liège > Département de chimie (sciences) > Chimie organométallique et catalyse homogène
Language :
English
Title :
Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors
Publication date :
2015
Journal title :
Beilstein Journal of Organic Chemistry
eISSN :
1860-5397
Publisher :
Beilstein-Institut
Volume :
11
Pages :
2318-2325
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 15 December 2015

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