Synthesis of 2-amino-imidazolium glycosides as precursors for novel chiral N-heterocyclic carbenes.

Synthesis of novel 2-amino-imidazolium glycosides in two steps from readily available tri-O-benzyl-d-glucal has been reported. Tri-O-benzyl-d-glucal was initially converted into 1,2-dideoxy-2-iodo-1-N-(p-toluenesulfonamido)-d-glucose following the procedure developed in our lab earlier, which on refluxing with various N-substituted imidazoles in acetonitrile resulted in a facile formation of 2-amino-imidazolium glycosides in excellent yields. The synthesis involves an initial formation of an unstable C-C aziridine ring which was followed by stereoselective attack of substituted imidazoles at the C position to afford 2-amino- imidazolium glycosides that also results in the transposition of amino group from C to C position. The reaction proceeds without the need of any activator; works with equal ease in presence of a variety of N-substituted imidazoles and the products could be obtained in pure form through multiple crystallization without the need for column chromatography. N-Heterocyclic carbenes derived from these 2-amino-imidazolium glycosides may find applications as new catalysts for enantioselective organic transformations.