Divergent Reactivity of δ-Acetoxy Allenoates with 1,3-Bisnucleophiles: Synthesis of Multisubstituted Pyran, Dihydropyran, and 3-Vinylpent-2-enedioate Scaffolds

Abstract Base-dependent synthesis of tetrasubstituted pyrans or 3,4-dihydropyrans using δ-acetoxy allenoates and enolizable carbonyls like cyclohexan-1,3-dione and ethyl benzoylacetate is reported. Thus, the use of DMAP as an organocatalytic base gives tetrasubstituted pyrans while DBU affords isomeric tetrasubstituted 3,4-dihydropyrans. The reaction of δ-acetoxy allenoates with ethyl benzoylacetate mediated by KO t Bu furnishes diethyl 3-vinylpent-2-enedioates.