Efficient synthesis of n-oxide derivatives:: Substituted 2-(2-(Pyridyl-N-oxide) methylsulphinyl) benzimidazoles

Different substituted 2-chloromethylpyridyl derivatives (6a-d) were oxidized with mCPBA to give the respective 2-chloromethylpyridine-N-oxide derivatives (7a-d) at low temperature, which on condensation with 2-mercapto-1H-benzimidazole (8a-c) in the presence of aprotic solvents give the 2-[[(pyridin-2-yl-1-oxide) methyl]sulfanyl]-1H-benzimidazole (9a-d) in good yield. Finally, 9a-d oxidized with mCPBA in chlorinated solvent gives a mixture of 2-[[(pyridin-2-yl-1-oxide) methyl]sulfonyl]-1H-benzimidazole (3a-d, 10%) and 2-[[(pyridin-2-yl-1-oxide) methyl] sulfinyl]1H-benzimidazole (4a-d, 90%) derivatives.