An efficient method for the generation of an oxidopyrylium ylide from 6-acetoxy-6-acetoxymethyl-2H-pyran-3(6H)-one using a Pd catalyst and [5+2] cycloadditions of the resulting ylide are described. Among substituted styrene derivatives as dipolarophiles, electron-rich styrenes showed higher yield (up to 80%). The [5+2] cycloaddition reactions can also be applied to exo-methylene cyclic compounds, and an improved method for the synthesis of polygalolide intermediate has been demonstrated.

中文翻译：

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使用Pd催化剂及其[5 + 2]环加成反应和几种偶极亲子试剂可高效生成氧化吡啶鎓叶立德

描述了使用Pd催化剂从6-乙酰氧基-6-乙酰氧基甲基-2 H-吡喃-3（6 H）-1生成氧化吡啶鎓叶立德的有效方法，以及所得的叶立德的[5 + 2]环加成。在取代的苯乙烯衍生物（如双极性亲和剂）中，富电子苯乙烯显示出更高的收率（高达80％）。[5 + 2]环加成反应也可以用于外亚甲基环状化合物，并且已经证明了一种改进的合成聚没食子酸酯中间体的方法。