Readily available chiral amine–thioureas are effective catalysts for the first diastereo- and enantioselective epoxidation of unsaturated pyrazolones. The trans- or cis-spiroepoxides are preferentially obtained in good yield and high to excellent enantioselectivity using an appropriate organocatalyst and tert-butyl hydroperoxide as the oxidant. The epoxidation appears applicable to highly challenging β,β′-substituted unsaturated pyrazolones, giving access to spiroepoxides bearing two vicinal quaternary stereocenters. The reaction represents a unique example of Weitz–Scheffer epoxidation, where the catalyst-controlled ring-closure step is usefully exploited to prepare both enantioenriched diastereomeric epoxides.

中文翻译：

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通过不饱和吡唑啉酮的有机催化环氧化非对映和对映选择性进入螺环氧化物

现成的手性胺-硫脲是不饱和吡唑啉酮的第一个非对映和对映选择性环氧化的有效催化剂。的反式-或顺式-spiroepoxides在良好收率和高使用适当的有机催化剂和优先获得优异的对映选择性叔丁基过氧化氢作为氧化剂。环氧化似乎适用于极富挑战性的β，β'-取代的不饱和吡唑啉酮，可接近带有两个邻位四元立体中心的螺环氧化物。该反应代表了Weitz-Scheffer环氧化的独特例子，其中催化剂控制的闭环步骤可用于制备两种对映体富集的非对映体环氧化物。