The First Example of an Unusual Rearrangement in the van Leusen Imidazole Synthesis.

The synthesis of an 1,4-disubstituted 5-methylimidazole is reported by reacting toluenesulfonylmethyl isocyanide with an enaminic tautomeric form of a secondary ketimine in the presence of catalytic amounts of bismuth(III) triflate. A possible mechanism involving a tosyl substitution on the imidazoline intermediate is proposed. This work represents a novel application for the versatile reagent toluenesulfonylmethyl isocyanide that expands its use to the preparation of imidazole starting from ketimine compounds.