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Biaryl Phosphites: New Efficient Adaptative Ligands for Pd-Catalyzed Asymmetric Allylic Substitution Reactions

机译:亚芳基亚磷酸酯:Pd催化的不对称烯丙基取代反应的新型高效适应性配体

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摘要

Pharmaceuticals, agrochemicals, fragrances, fine chemi-ncals, and natural product chemistry all rely on thenpreparation of enantiomerically enriched compounds. Thenpalladium-catalyzed asymmetric allylic substitution, whichnallows for the enantioselective formation ofncarbon carbon and carbon heteroatom bonds, is anpotential synthetic tool for preparing these compounds. Tondate, most of the successful ligands reported for the Pd-ncatalyzed allylic substitution reactions have used threenmain design strategies. The first, developed by Hayashi and co-workers, used a secondary interaction of the nucleo-nphile with a side chain of the ligand to direct the approach of the nucleophile to one of the allylic terminal carbonnatoms. The second increased the ligand’s bite angle in order to create a chiral cavity in which the allyl system is per-nfectly embedded. To discriminate electronically between the two allylic terminal carbon atoms, the third strategynemployed heterodonor ligands. Although many chiral ligands have been successfully applied in the substitution of sev-neral disubstituted substrates, problems generally remain with both substrate specificity and reaction rates using thesenmethods. Other substrates, such as those that are monosubstituted, will require more active and more regio- and enan-ntioselective Pd-catalysts. Overcoming these limitations requires research toward the development of new ligands.nThis Account discusses the application of homo- and heterodonor biaryl-containing phosphites as new, versatile,nand highly effective ligands in the Pd-catalyzed asymmetric allylic substitution of several substrate types. We and oth-ners recently demonstrated that the inclusion of biarylphosphite moieties in ligand design is highly advantageous. Innthese systems, the catalyst’s substrate specificity decreases because the chiral pocket created (the chiral cavity withnthe embedded allyl ligand) is flexible enough to allow the perfect coordination of hindered and unhindered sub-nstrates. Reaction rates with these ligands increase because of the larger π-acceptor ability of these moieties. The abil-nity of the phosphite moiety to accept π-electrons and enhance the SN1 character of the nucleophilic attack increasesnthe regioselectivity of the reactions toward the desired branched isomer in monosubstituted linear substrates. Finally,nthe easy synthesis of biaryl phosphites from readily available alcohols allows for simple ligand tuning as well as sys-ntematic modifications of several important ligand parameters.
机译:药品,农用化学品,香料,精细化学药品和天然产物化学都依赖于对映体富集化合物的制备。然后,钯催化的不对称烯丙基取代,这是碳碳和碳杂原子键的对映选择性形成,是制备这些化合物的潜在合成工具。迄今为止,已报道的大多数用于Pd催化的烯丙基取代反应的成功配体都使用了三种主要的设计策略。由Hayashi及其同事开发的第一个化合物,利用亲核试剂与配体侧链的二次相互作用将亲核试剂引导至一个烯丙基末端碳原子上。第二个增加了配体的咬合角,以创建一个手性腔,其中烯丙基系统完美地嵌入其中。为了电子区别两个烯丙基末端碳原子,第三个策略采用了杂原子供体。尽管许多手性配体已成功地用于取代几种双取代底物,但底物特异性和使用该方法的反应速率通常仍​​然存在问题。其他底物,例如单取代的底物,将需要更多的活性以及更多的区域和对位选择性的Pd催化剂。要克服这些局限性,就需要研究开发新的配体。n此帐户讨论了含同型和杂配体联芳基的亚磷酸酯作为新型,通用,高效配体在Pd催化的几种底物类型的不对称烯丙基取代中的应用。我们和其他人最近证明,在配体设计中包含亚磷酸二芳基酯部分是高度有利的。在这些系统中,催化剂的底物特异性降低,因为所形成的手性袋(具有嵌入的烯丙基配体的手性腔)足够柔韧性,可以使受阻和不受阻的底物完美地配合。由于这些部分的更大的π-受体能力,与这些配体的反应速率增加。亚磷酸酯部分接受π电子并增强亲核攻击的SN1特性的能力提高了反应在单取代线性底物中对所需支链异构体的区域选择性。最后,从容易获得的醇中轻松合成亚磷酸亚芳基酯允许简单的配体调节以及对几个重要配体参数的系统修饰。

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  • 来源
    《Accounts of Chemical Research》 |2010年第2期|p.312-322|共11页
  • 作者单位

    Departament de Quı ´mica Fı ´sica i Inorga `nica, Universitat Rovira i Virgili,C/ Marcel · lı ´ Domingo s, 43007 Tarragona, Spain;

  • 收录信息 美国《科学引文索引》(SCI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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  • 正文语种 eng
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  • 入库时间 2022-08-17 13:24:22

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