[(<i>p</i>-Cymene)RuCl<sub>2</sub>]<sub>2</sub>: An Efficient Catalyst for Highly Regioselective Allylic Alkylations of Chelated Amino Acid Ester Enolates
作者:Anton Bayer、Uli Kazmaier
DOI:10.1002/chem.201402825
日期:2014.8.11
are excellent nucleophiles for ruthenium‐catalyzed allylic alkylations. Although [Cp*Ru(MeCN)3]PF6 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)RuCl2]2 allowed allylations to be performed with a high degree
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,但生成的烯丙基络合物在低至-78°C的温度下反应,但不幸的是,该过程仅在区域和非对映选择性中等。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。这个自由异构化协议也可以被用于(合成Ž)构型γ,δ不饱和氨基酸衍生物,从(起始ž)-烯丙基底物。在这里,发现活性更高的磷酸盐优于羧酸盐,以几乎定量的产量提供所需的氨基酸,并具有良好的区域和立体保留能力。因此,Ru催化的烯丙基化反应可以很好地克服Pd催化方法的缺点。