Intramolecular oxidopyrylium-based [5 + 2] cycloadditions utilizing chiral auxiliaries were investigated. Both acetoxypyranones and silyloxypyrones were employed and sulfinimines, oxazolidinones, hydrazones, and chiral enamines were explored. Carbonyl-based auxiliaries gave low selectivity, but enamines afforded excellent diastereoselectivity. Overall, facial selectivity varied significantly providing insight regarding the scope and limitation of chiral auxiliary-based oxidopyrylium-alkene [5 + 2] cycloadditions.

中文翻译：

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分子内不对称基于氧化吡啶鎓的[5 + 2]环加成

利用手性助剂研究了基于分子内氧化吡啶基的[5 + 2]环加成反应。乙酰氧基吡喃酮和甲硅烷氧基吡喃酮均被使用，并研究了亚磺胺，恶唑烷酮，和手性烯胺。基于羰基的助剂具有较低的选择性，但烯胺具有出色的非对映选择性。总体而言，面部选择性变化很大，从而提供了有关基于手性助剂的氧化吡啶烯-烯烃[5 + 2]环加成反应的范围和限制的见解。