Palladium catalyzed allylic alkylations of nonstabilized enolates
Palladium catalyzed allylic alkylations of nonstabilized enolates
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DOI：
10.2174/1385272033372888
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发表时间：
2003-03-01
影响因子：
2.6
通讯作者：
Kazmaier, U
中科院分区：
文献类型：
--
作者：
Kazmaier, U
钯催化的烯丙基烷基化反应是有机合成中的重要反应。一般来说，稳定的碳负离子用作软C-亲核试剂。不稳定的酮和酯的烯醇化物经常引起问题，本文综述了这些有趣的亲核试剂的发展和改进.对于酮的烯醇化物，用相应的锡衍生物得到最好的结果，但也可以使用烯氧基硼酸酯.用酮烯醇化物得到α-烯丙基化产物。在合适的手性配体存在下，得到具有高立体选择性的光学活性取代产物。相反，空间位阻酯烯醇化物不提供烯丙基化产物，但产生环丙烷衍生物。这可以通过烯醇化物攻击中间体形成的π-烯丙基络合物的中心碳原子来解释。相反，如果甲硅烷基烯酮缩醛用作亲核试剂，或乙烯基环氧化物用作烯丙基底物，则α-烯丙基化产物。得到了这也适用于或多或少稳定的衍生自吡嗪酮或吖内酯的烯醇化物，产生α-烷基化氨基酸衍生物。“正常”不饱和氨基酸可以通过使用螯合的氨基酸酯烯醇化物作为亲核试剂来获得。该烯醇化物显示出高反应性，因此这些反应可以在非常温和的条件下进行，在该条件下可以抑制π-烯丙基中间体的π-σ-π-异构化。这开辟了全新的合成可能性。在手性配体的存在下，获得光学活性氨基酸。
Palladium catalyzed allylic alkylations are important reactions in organic synthesis. In general stabilized carbanions are used as soft C-nucleophiles. Nonstabilized enolates from ketones and esters often cause problems, and the developments and improvements made with these interesting nucleophiles are summarized in this review.With respect to ketone enolates, best results are obtained with the corresponding tin derivatives, but enoxybo-rates also can be used. With ketone enolates alpha-allylated products are obtained. In the presence of suitable chiral ligands, the optically active substitution products are obtained with high stereoselectivity. In contrast, sterically hindered ester enolates do not provide allylation products, but give rise to cyclopropane derivatives. This can be explained by an attack of the enolate at the central carbon atom of the intermediatly formed pi-allyl complex. In contrast, if silylketene acetals are used as nucleophiles, or vinylepoxides as allylic substrates, the alpha-allylated products are. obtained. This is also true with more or less stabilized enolates derived from pyrazinones or azlactones, giving rise to alpha-alkylated amino acid derivates. "Normal" unsaturated amino acids can be obtained by using chelated amino acid ester enolates as nucleophiles. This enolates show a high reactivity and therefore these reactions can be carried out under very mild conditions, conditions under which the pi-sigma-pi-isomerization of the pi-allyl intermediates can be suppressed. This opens up totally new synthetic posibilities. In the presence of chiral ligands optically active amino acids are obtained.