Regioselective Syntheses of Functionalized 2-Aminopyridines and 2-Pyridinones through Nucleophile-Induced Ring Transformation Reactions

An efficient one-pot synthesis of 2-amino-6-aryl-4-methylsulfanylpyridines and 6-aryl-3-cyano-4-methylsulfanyl-2(1H)pyridinone has been illustrated through ring transformation of 6-aryl-3-cyano-4-methylsulfanyl-2H-pyran-2-ones by urea through different reaction conditions. Various solvents and bases were employed to selectively prepare either 2aminopyridines or 2-pyridinones. In case of direct fusion of 2H-pyran-2-one with urea in solvent-free conditions, both the products were obtained in 1:1 ratio, while the reaction in pyridine at reflux temperature exclusively afforded 2-aminopyridine in 80-90% yield. The reaction of 6-aryl-3-carbomethoxy-4-methylsulfanyl-2H-pyran-2-ones with urea at 150 °C afforded 2-pyridinone derivatives in good yield (70-80%).