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首页> 外文期刊>Chemistry: A European journal >[(p-Cymene)RuCl_2]_2: An Efficient Catalyst for Highly Regioselective Allylic Alkylations of Chelated Amino Acid Ester Enolates
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[(p-Cymene)RuCl_2]_2: An Efficient Catalyst for Highly Regioselective Allylic Alkylations of Chelated Amino Acid Ester Enolates

机译：[（p-Cymene）RuCl_2] _2：螯合氨基酸酯烯醇化物的高区域选择性烯丙基烷基化的高效催化剂

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摘要

Chelated amino acid ester enolates are excellent nucleophiles for ruthenium-catalyzed allylic alkylations. Although [Cp*Ru(MeCN)_3]PF_6 was found to be the most reactive catalyst investigated, with the resulting allyl complexes reacting at temperatures as low as -78°C, unfortunately the process took place with only moderate regio- and diastereoselectivity. In contrast, [(p-cymene)RuCl_2]_2 allowed allylations to be performed with a high degree of regioretention. Secondary allyl carboxylates with a terminal double bond were found to be the most reactive substrates, giving rise to the branched amino acids with perfect regioretention and chirality transfer. In this case, no isomerization of the Ru–allyl complex formed in situ was observed, in contrast to the analogues palladium complexes. This isomerization-free protocol can also be used for the synthesis of (Z)-configured γ,δ-unsaturated amino acid derivatives, starting from (Z)-allylic substrates. Here, the more reactive phosphates were found to be superior to the carboxylates, providing the required amino acids in almost quantitative yield with perfect regioand stereoretention. Therefore, the Ru-catalyzed allylation reactions are well positioned to overcome the drawbacks of Pd-catalyzed processes.
机译：螯合的氨基酸酯烯醇盐是钌催化的烯丙基烷基化反应的优良亲核试剂。尽管发现[Cp * Ru（MeCN）_3] PF_6是最活泼的催化剂，但所得的烯丙基络合物在低至-78°C的温度下反应，但不幸的是，该过程仅发生了中等的区域和非对映选择性。相反，[（p-cymene）RuCl_2] _2允许烯丙基化具有高度的区域保留性。发现具有末端双键的仲烯丙基羧酸盐是反应性最强的底物，产生具有完美的区域保留和手性转移的支链氨基酸。在这种情况下，与类似物钯配合物相比，未观察到原位形成的Ru-烯丙基配合物的异构化。这种无异构化的方案也可以用于从（Z）烯丙基底物开始合成（Z）-构型的γ，δ-不饱和氨基酸衍生物。在这里，发现反应性更高的磷酸盐优于羧酸盐，以几乎定量的产率提供所需的氨基酸，并具有良好的区域和立体保持性。因此，Ru催化的烯丙基化反应被很好地定位以克服Pd催化的方法的缺点。

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