Crystalline derivatives of the following l-amino acids modified by 3,5-dinitro-4-pyridone have been prepared: glycine, alanine, valine, leucine, isoleucine, phenylalanine, serine, threonine, tyrosine, aspartic acid, asparagine, glutamic acid, glutamine, tryptophan, histidine, arginine, methionine and lysine. The modified l-amino acids (DNPY-l-amino acids) could be purified by recrystallization and were characterized by 1H-NMR, IR and UV spectral data. The molar rotation of the DNPY-l-amino acids varied from 2 to 100 times those of the parent amino acids. The effectiveness of 3,5-dinitro-1-(4-nitrophenyl)-4-pyridone as an amino-protecting reagent of l-amino acids is described.

The Reissert-Kaufmann-type reaction of substituted N-methoxy-4-nitropyridinium methylsulfates gave the corresponding 2-cyano-4-nitropyridines in satisfactory yields. When 3-methyl-4-nitropyridine N-oxide was used as the starting material, a cyano group was introduced not into the 6-position, but into the 2-position. This preference may be explained by proposing a hyperconjugation effect of the 3-methyl group. The resulting nitriles were quantitatively hydrolyzed to the corresponding 4-nitropicolinic acids. These reactions provided a new route for the preparation of nitropyridinecarboxylic acids from pyridine homologues. Further, some nucleophilic substitution reactions of the products were carried out.

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A novel ring transformation is found in a series of reactions of 1-substituted 3,5-dinitro-2-pyridones, electron-deficient substrates, with monosodium salts of β-keto esters. A variety of 1-substituted 3,5-dinitro-2-pyridones are treated with diethyl sodio-3-oxopentanedioate and ethyl sodioacetoacetate to give, in addition to N-substituted nitroacetamides (3), 2,6-bis(ethoxycarbonyl)-4-nitrophenol (2), and 2-ethoxycarbonyl-4-nitrophenol (4) respectively. The bicyclic intermediates, 2-azabicyclo[3.3.1]nona-3,7-dienes, can be isolated on the reaction of 3,5-dinitro-1-methyl-2-pyridone at room temperature. The phenol derivatives (2 and 4) may consist of the reagent and a C4–C5–C6 moiety of the parent pyridone, while N-substituted nitroacetamides, 3, may result from the other fragment, N–C2–C3, of the pyridone. A probable course of the reaction, involving the step-by-step nucleophilic attack of the ambident nucleophiles, sodio β-keto esters, at the ambident electrophilic centers of 2-pyridones to form bicyclic intermediate, is proposed.

Fragmentation of 3,5-dinitro-2-pyridone (1) by primary amine gave nitroacetamide (2) and nitromalonaldehyde diimine. In the case of N-methyl derivative (1c), the reaction was completely suppressed by the product 2 to give an anionic σ-adduct of 1c with 2. The mechanism of the reaction was discussed.