Efficient generation and amplification of chirality from prochiral substrates in the Diels–Alder reaction (DA reaction) followed by dynamic crystallization were achieved without using an external chiral source. Since the DA reaction of 2-methylfuran and various maleimides proceeds reversibly, an exo-adduct was obtained as the main product as the reaction proceeded. From single crystal X-ray structure analysis, it was found that five of ten exo-adducts gave conglomerates. When 2-methylfuran and various maleimides with a catalytic amount of TFA were reacted in a sealed tube, the exo-DA adducts were precipitated from the solution, while the reaction mixtures were continuously ground and stirred using glass beads. Deracemization occurred and chiral amplification was observed for four of the substrates. Each final enantiomeric purity was influenced by the crystal structure, and when enantiomers were included in the disorder, they reached an enantiomeric purity reflecting the ratio of the disorder. The final ee value of the 3,5-dimethylphenyl derivative after chiral amplification was 98% ee.

中文翻译：

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涉及 Diels-Alder 反应中手性对称性破坏的绝对不对称合成

在不使用外部手性源的情况下，在 Diels-Alder 反应（DA 反应）中从前手性底物有效生成和放大手性，然后进行动态结晶。由于 2-甲基呋喃与各种马来酰亚胺的 DA 反应可逆进行，随着反应的进行，主要产物为外加合物。从单晶 X 射线结构分析中，发现 10 个外加合物中有 5 个形成了聚结物。当 2-甲基呋喃和各种马来酰亚胺与催化量的 TFA 在密封管中反应时，exo-DA 加合物从溶液中沉淀出来，同时使用玻璃珠连续研磨和搅拌反应混合物。发生去外消旋化并且观察到四种底物的手性扩增。每个最终的对映体纯度都受晶体结构的影响，当对映体包含在无序中时，它们会达到反映无序比例的对映体纯度。手性扩增后3,5-二甲基苯基衍生物的最终ee值为98% ee。