Synthesis of imidazole derivatives using 2-unsubstituted 1H-imidazole 3-oxides

Abstract

The reaction of 1,4,5-trisubstituted 1H-imidazole 3-oxides 1 with Ac2O in CH2Cl2 at 0 - 5° leads to the corresponding 1,3-dihydro-2H-imidazol-2-ones 4 in good yields. In refluxing Ac2O, the N-oxides 1 are transformed to N-acetylated 1,3-dihydro-2H-imidazol-2-ones 5. The proposed mechanisms for these reactions are analogous to those for N-oxides of 6-membered heterocycles (Scheme 2). A smooth synthesis of 1H-imidazole-2-carbonitriles 2 starting with 1 is achieved by treatment with trimethylsilanecarbonitrile (Me3SiCN) in CH2Cl2 at 0 - 5° (Scheme 3).