Synthesis and Heterodiene Condensation Reactions of Dihydropyrans of the Acetylene Series

Dihydropyrans containing acetylene moieties and reactive side-chain functional groups represent versatile building blocks in modern organic synthesis and heterocyclic chemistry. In this study, we report the synthesis of novel acetylenic dihydropyran derivatives via the heterodienne condensation (Diels–Alder reaction) of α,β-unsaturated aldehydes (acrolein and crotonic aldehyde) with allylacetylene alcohol and its derivatives. Reaction conditions—including component ratios, temperature (175–180°C), and reaction duration—were optimized to control the regioselective formation of mono-adducts (I–IV) and bis-adducts (V–VIII). Furthermore, the reactivity of the synthesized acetylenic dihydropyrans was investigated under retro-Favorsky reaction conditions (alkaline cleavage with powdered KOH in the presence of acetone), successfully yielding dihydropyrans bearing terminal acetylene functionalities (IX, X). All synthesized structures were comprehensively characterized using 1H/13C NMR, FTIR spectroscopy, and elemental analysis. These acetylenic heterocyclic scaffolds demonstrate high potential as precursors for bioactive compounds, antiviral derivatives, and functional monomeric units for specialized polymers.