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.

中文翻译：

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δ-乙酰氧基联烯酸酯与 1,3-双亲核试剂的不同反应性：多取代吡喃、二氢吡喃和 3-乙烯基戊-2-烯二酸酯支架的合成

据报道，使用 δ-乙酰氧基联烯酸酯和可烯醇化羰基（例如环己烷-1,3-二酮和苯甲酰乙酸乙酯）依赖碱基合成四取代吡喃或 3,4-二氢吡喃。因此，使用DMAP作为有机催化碱得到四取代的吡喃，而DBU则得到异构的四取代的3,4-二氢吡喃。^{δ-乙酰氧基联烯酸酯与苯甲酰乙酸乙酯在 KO t} Bu介导下反应生成3-乙烯基戊-2-烯二酸二乙酯。