Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr.HCl, IMes.HCl and IXy.HCl.
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.
Hintermann
Lukas
L
Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, D-52074 Aachen, Germany. lukas.hintermann@oc.rwth-aachen.de