The Nucleophilic Reaction of Electron-deficient Pyridone Derivatives. I. The Ring Transformation of 1-Substituted 3,5-Dinitro-2-pyridones with Sodio β-Keto Esters

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.