Polyketo-enols and chelates. Synthesis of 2-pyrones, 2-pyridones, 2-methoxypyridines, and m-hydroxyanilines by control of the cyclisation of nitrile-substituted glutaconic types

Abstract

Sodium methoxide-initiated condensation between methyl cyanoacetate and methyl methoxymethyleneacetoacetate leads, via a nitrite-substituted propene (glutaconic ester), to a 2-pyridone at low base molarities and to a 2-pyrone at high ones. Employment of high molarities of magnesium methoxide gives, in addition, a m-hydroxyaniline. When malononitrile replaces methyl cyanoacetate a 2-methoxypyridine is also formed at high methoxide molarities.

Various examples of these nitrile reactions, which have synthetic potential, are surveyed. Formation of the products (controllable in terms of the nature and molarity of base, nature of substituents, and time and temperature of reaction) can be interpreted as a series of equilibria in which the nitrile-substituted propenes and imino-lactones are central, and the pyridones, alkoxypyridines, and hydroxyanilines are formed irreversibly.