Synthetic approaches to imidazo [4,5-b] and [4,5-c]pyridine-1 and/or 3-oxides

Abstract

In Chapter 1, the syntheses of some known heterocyclic-N-oxides viz. purine-N-oxides, benzotriazole-N-oxides, benzimidazole-N-oxides and imidazopyridine-N-oxides, are discussed in varying degrees of depth. Some of the biological properties of these compounds are mentioned. In Chapter 2, the reactions with bases of 3-amino-2-nitro and 2-amino-3-nitropyridine derivatives are studied. 2-p-Nitrophenyl-lH-imidazo[4,5-b]pyridine-3-oxide is obtained in high yield by the base-induced cyclisations of 2-nitro-3-N-p-nitrobenzylaminopyridine. The base reactions of the N-ethoxycarbonyl, N-methanesul phonyl and N-p-toluenesulphonyl derivatives of 2-nitro-3-N-p-nitrobenzylaminopyridine also yield the 3-oxide but in lower yield along with other products such as p-nitrobenzoic acid and/or 2-p-nitrophenylimidazo[4,5-b]- pyridine. 2-p-Nitrophenyl-3H-imidazo[4,5-b]pyridine-l-oxide is obtained by the corresponding reactions of bases with 3-nitro-2-N-p-nitrobenzylaminopyridine. Cleavage is the main reaction when 3-N-methanesulphonyl-N-phenacylamino-2-nitropyridine is treated with bases. When the base used is aqueous ammonia, the major products of the reaction are 3-N-methanesulphonylamino-2-nitropyridine and 2-benzoyl-4(5)-phenylimidazole. Various mechanisms to account for these results are discussed. Also studied in this chapter is the reaction of pyridofuroxan with ethyl acetoacetate in the presence of various bases. In Chapter 3, the reactions with sodium methoxide of the p-toluenesulphonyl derivative of 3-nitro-4-N-p-nitrobenzylaminopyridine and 3-nitro-4- N-phenacylaminopyridine are studied. The identified products of these reactions are cleavage products and the various mechanisms to account for these results are discussed. The attempted syntheses of some other 4-amino-3-nitropyridine derivatives are also discussed.