Ring Transformations of 2H-Pyran-2-ones and Fused Pyran-2-ones with Nucleophilic Reagents

In this review we report on several recently described nitrogen-and carbon-nucleophile-induced ring transformations of selected pyran-2-one derivatives.These reactions provide convenient routes for the synthesis of different heterocycles and carbocycles as well as NITROGEN-NUCLEOPHILE-INDUCED RING TRANSFORMATIONS OF 2H-PYRAN-2-ONESAND FUSED PYRAN-2-ONES 5,6,7,8-Tetrahydro-2H-1-benzopyran-2,5-diones (2) 3 were converted with ammonia, hydroxylamine, aniline, amino acids, hydrazine and N,N-dimethylhydrazine in boiling ethanol into 2,5-dioxo-1,2,5,6,7,8-hexahydroquinolines (3) (Scheme 1). 4 By heating the benzopyrans (2) with an excess of hydrazine hydrate the reaction took place at the pyranone ring and at the 5-oxo group, and even debenzoylation of the benzoylamino group occurred, yielding 3-amino-5-hydrazonoquinolinones (4).