Chiral Anion-Mediated Asymmetric Ring Opening of meso-Aziridinium and Episulfonium Ions
Chiral Anion-Mediated Asymmetric Ring Opening of meso-Aziridinium and Episulfonium Ions
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DOI：
10.1021/ja806431d
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发表时间：
2008-11-12
影响因子：
15
通讯作者：
Toste, F. Dean
中科院分区：
文献类型：
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作者：
Hamilton, Gregory L.;Kanai, Toshio;Toste, F. Dean
通过缺乏刘易斯或布朗斯台德碱性位点的阳离子中间体进行的反应对基于手性金属或有机催化剂的传统不对称催化提出了挑战。我们提出了一个对映选择性开环的四取代的meso-aziridinium离子与醇亲核试剂进行通过手性离子对与联萘酚磷酸阴离子。该反应是由银诱导的β-氯胺闭环使用的银盐的手性阴离子作为原位生成的催化剂。使用不溶性的Ag 2CO 3作为银源对于获得高的对映体选择性是必不可少的;我们认为手性磷酸盐充当“手性阴离子相转移催化剂”，将银离子带入有机相中。手性阴离子的概念也可以扩展到相关的不对称开放的meso-episulfonium离子产生的三氯乙酰亚胺邻近硫化物的质子化。
Reactions proceeding through cationic intermediates that lack a Lewis or Bronsted basic site present a challenge for traditional asymmetric catalysis based on chiral metals or organocatalysts. We present an enantioselective ring opening of tetrasubstituted meso-aziridinium ions with alcohol nucleophiles proceeding through a chiral ion pair with a binaphthol-phosphate anion. The reaction is initiated by silver-induced ring closure of beta-chloroamines using the Ag salt of the chiral anion as in situ generated catalyst. Use of insoluble Ag2CO3 as silver source is essential to obtain high enantioselectivity; we believe the chiral phosphate acts as a chiral anion phase transfer catalyst" to bring silver ion into the organic phase. The chiral anion concept can also be extended to the related asymmetric opening of meso-episulfonium ions generated by protonation of trichloroacetimidates vicinal to sulfides.