Enantioselective synthesis of allylboronates bearing a tertiary or quaternary B-substituted stereogenic carbon by NHC-Cu-catalyzed substitution reactions.
Enantioselective synthesis of allylboronates bearing a tertiary or quaternary B-substituted stereogenic carbon by NHC-Cu-catalyzed substitution reactions.
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DOI：
10.1021/ja104254d
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发表时间：
2010-08-11
影响因子：
15
通讯作者：
Hoveyda, Amir H.
中科院分区：
文献类型：
--
作者：
Guzman-Martinez, Aikomari;Hoveyda, Amir H.
烯丙基取代提供了带有B-取代的叔或季碳立体中心的α-取代的烯丙基硼酸酯。C-B键形成反应，由手性双齿Cu-NHC络合物催化，在市售的双（频哪醇合）二硼的存在下进行。转化以高产率（高达>98%）、位点选择性（> 98%SN 2 ′）和高达>99：1的对映体比（er）进行。可以使用反式以及顺式二取代的烯烃;烷基-（直链以及支链）和芳基取代的三取代烯丙基碳酸酯用作有效底物。带有季碳中心的烯丙基硼酸酯是空气稳定的，并且可以容易地通过硅胶色谱法纯化;相反，仲烯丙基硼酸酯不能以相同的方式纯化，并且稳定性明显较低。对映体富集的产物的氧化除去了仲或叔烯丙醇，这些有价值的小分子不能通过替代合成或动力学拆分方法以高对映体纯度容易地获得。
Allylic substitutions that afford α-substituted allylboronates bearing B-substituted tertiary or quaternary carbon stereogenic centers are presented. C–B bond forming reactions, catalyzed by chiral bidentate Cu–NHC complexes, are performed in the presence of commercially available bis(pinacolato)diboron. Transformations proceed in high yield (up to >98%), site selectivity (>98% SN2′) and in up to >99:1 enantiomer ratio (er). Trans as well as cis disubstituted alkenes can be used; alkyl- (linear as well as branched) and aryl-substituted trisubstituted allylic carbonates serve as effective substrates. Allylboronates that bear a quaternary carbon center are air-stable and can be easily purified by silica gel chromatography; in contrast, secondary allylboronates cannot be purified in the same manner and are significantly less stable. Oxidation of the enantiomerically enriched products furnishes secondary or tertiary allylic alcohols, valuable small molecules that cannot be easily obtained in high enantiomeric purity by alternative synthesis or kinetic resolution approaches.
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