Nucleophilic reaction upon electron-deficient pyridone derivatives. XIII. Regioselective synthesis of 2-substituted 3-nitropyridines by one-pot reaction of either 4- or 6-substituted 1-methyl-3,5-dinitro-2-pyridones with ketones and ammonia

Article abstract of DOI:10.1246/bcsj.67.2176

A one-pot synthesis of 2-substituted 3- nitropyridines was developed by a ring transformation of 6- or 4-substituted 1-methyl-3,5-dinitro-2-pyridones (2 or 3) with ammonia and enamines derived from ketones. Some intermediates having a 2,6-diazabicyclo[3.3.1]nonane skeleton were isolated from reactions of 3. The ring transformation proceeds via an addition-addition-elimination-elimination mechanism. Few competitive isomeric by-products, 4-substituted 3-nitropyridines and 4-nitroanilines, were formed. All the 2 substrates showed good reactivity, but the 3 substrates having electron-withdrawing substituents were less reactive and selective. 1,4,6-Trimethyl-3,5-dinitro-2-pyridone did not give any products. The selectivity is interpreted in terms of differences of thermodynamic (main selection rule B) and kinetic stability (minor selection rule A) between the possible bicyclic intermediates which are expected to be formed via the mechanism.