TY - JOUR A1 - Hintermann, Lukas T1 - Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl JF - Beilstein Journal of Organic Chemistry PY - 2007/// VL - 3 SP - 22 SN - 1860-5397 DO - 10.1186/1860-5397-3-22 PB - Beilstein-Institut JA - Beilstein J. Org. Chem. UR - https://doi.org/10.1186/1860-5397-3-22 N2 - The 1,3-diaryl-imidazolium chlorides IPr·HCl (aryl = 2,6-diisopropylphenyl), IMes·HCl (aryl = 2,4,6-trimethylphenyl) and IXy·HCl (aryl = 2,6-dimethylphenyl), precursors to widely used N-heterocyclic carbene (NHC) ligands and catalysts, were prepared in high yields (81%, 69% and 89%, respectively) by the reaction of 1,4-diaryl-1, 4-diazabutadienes, paraformaldehyde and chlorotrimethylsilane in dilute ethyl acetate solution. A reaction mechanism involving a 1,5-dipolar electrocyclization is proposed. ER -