Synthesis of Substituted 5,6-Dihydro-2H-pyran-2-ones. Propiolic Acid Dianion as a Reactive Three-Carbon Nucleophile

Substituted 5,6-dihydro-2H-pyran-2-ones of four basic structural types (I-IV) were synthesized by addition reactions to derivatives of δ-hydroxyacetylenic acids 3. The acetylenic acids were, in turn, obtained by the reaction of the propiolic acid dianion with epoxides. The addition of methanol, hydrogen, and dialkylcuprates generated three types of dihydropyrones related to biologically active compounds, while the subsequent alkylation or acylation of the vinyl anion derived from dialkylcuprate addition provided a route to the fourth structural type possessing substitution at C-3.