Dipartimento di Chimica e Biologia "A. Zambelli", Università di Salerno , Via Giovanni Paolo II, 84084 Fisciano, Italy.
Department of Chemistry, Aarhus University , Langelandsgade 140, 8000 Aarhus, Denmark.
Org Lett. 2017 Oct 6;19(19):5030-5033. doi: 10.1021/acs.orglett.7b02189. Epub 2017 Sep 14.
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.
手性胺-硫脲可 readily available 作为有效的催化剂，用于不饱和吡唑酮的首例非对映选择性和对映选择性环氧化反应。trans- 或 cis-螺环氧化物可以高产率和高至优异的对映选择性获得，使用适当的有机催化剂和叔丁基过氧化氢作为氧化剂。该环氧化反应似乎适用于极具挑战性的β,β'-取代的不饱和吡唑酮，能够得到带有两个相邻季立体中心的螺环氧化物。该反应代表了 Weitz-Scheffer 环氧化反应的一个独特例子，其中催化剂控制的闭环步骤被有效地利用来制备两种对映体富集的非对映异构体环氧化物。
