NUCLEOPHILIC REACTION UPON ELECTRON-DEFICIENT PYRIDONE DERIVATIVES .13. REGIOSELECTIVE SYNTHESIS OF 2-SUBSTITUTED 3-NITROPYRIDINES BY ONE-POT REACTION OF EITHER 4-SUBSTITUTED OR 6-SUBSTITUTED 1-METHYL-3,5-DINITRO-2-PYRIDONES WITH KETONES AND AMMONIA

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-p yridones (2 or 3) with ammonia and enamines derived from ketones. Some intermediates having a 2,6-diazabicyclo[3.3.1]nonane skeleton were is olated from reactions of 3. The ring transformation proceeds via an ad dition-addition-elimination-elimination mechanism. Few competitive iso meric by-products, 4-substituted 3-nitropyridines and 4-nitroanilines, were formed. All the 2 substrates showed good reactivity, but the 3 s ubstrates having electron-withdrawing substituents were less reactive and selective. 1,4,6-Trimethyl-3,5-dinitro-2-pyridone did not gave any products. The selectivity is interpreted in terms of differences of t hermodynamic (main selection rule B) and kinetic stability (minor sele ction rule A) between the possible bicyclic intermediates which are ex pected to be formed via the mechanism.