Enantioselective cascade radical addition-cyclization-trapping reactions.
Enantioselective cascade radical addition-cyclization-trapping reactions.
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DOI：
10.1002/anie.200602042
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发表时间：
2006-09
影响因子：
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通讯作者：
H. Miyabe;R. Asada;Akira Toyoda;Y. Takemoto
中科院分区：
文献类型：
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作者：
H. Miyabe;R. Asada;Akira Toyoda;Y. Takemoto
近年来，对映选择性自由基反应的研究取得了一些显着的成功，[1]特别是在分子间加成反应，烯丙基化和H-原子转移反应中。[2，3]相反，只有少数报道描述了对映选择性自由基环化，其可以根据与刘易斯酸的配位性质分为三种类型（I-III，方案1）。[4-7]在II型环化反应中，使用由b-酮酸酯作为配位位点产生的aradical物种实现了高度的立体控制，并被Yang及其同事应用于级联环化。[7]然而，目前还没有报道涉及分子内和分子间的CCl 3C键形成过程的对映选择性级联反应。在此，我们报告了一个级联IV型战略，利用异羟肟酸酯。[5，8]由于大多数自由基反应都是通过早期过渡态进行的，底物的结构起着重要的作用;[9]因此，控制旋转异构体的数量对于在级联反应中实现高选择性至关重要。我们认为，主要形成单一的反应，
In recent years, studies on enantioselective radical reactions have achieved some remarkable success,[1] particularly in intermolecular addition reactions, allylations, and H-atom transfer reactions.[2, 3] In contrast, only a handful of reports describe enantioselective radical cyclizations, which can be classified into three types by the nature of the coordination with a Lewis acid (I–III, Scheme 1).[4–7] A high degree of stereocontrol was achieved in type II cyclizations using aradical species generated from a b-keto ester as a coordination site and was applied to cascade cyclization by Yang and co-workers.[7] However, there are no reports on enantioselective cascade reactions involving both inter-and intramolecular CÀC bond-forming processes. Herein, we report a cascade type IV strategy that takes advantage of the hydroxamate ester.[5, 8]As most radical reactions proceed through early transition states, the structure of the substrate plays an important role;[9] thus, the control of the rotamer population would be crucial for achieving high selectivity in cascade reactions. We consider that the predominant formation of a single reactive