Department of Chemistry & Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, USA.
J Am Chem Soc. 2011 Mar 2;133(8):2410-3. doi: 10.1021/ja1112518. Epub 2011 Feb 3.
We present a 6-NHC-Cu(I) complex that provides α-substituted allylboronates using allylic aryl ether substrates. The method was discovered by comparison of the chemoselectivities exhibited by complexes 1a, 1b, 2, and 3. We observed that 1a preferentially reacts with electron-rich alkenes over electron-deficient alkenes. Development of an asymmetric method revealed that 1b reacts with both the E and Z isomers to provide the same absolute configuration without showing E-Z isomerization. This stereoconvergent reaction occurs with high yields (av 86%), high S(N)2' selectivity (>99:1), and high ee (av 94%) and exhibits wide functional-group tolerance using pure E or Z isomer or E/Z alkene mixtures. The stereoconvergent feature enables the use of many different olefination strategies for substrate production, including cross-metathesis. Chiral allylboronates could be purified by silica gel chromatography and stored in the freezer without decomposition.
我们提出了一种 6-NHC-Cu(I) 配合物，它可以使用烯丙基芳基醚底物提供α-取代的烯丙基硼酸酯。该方法是通过比较配合物 1a、1b、2 和 3 表现出的化学选择性发现的。我们观察到 1a 优先与富电子烯烃反应，而不是缺电子烯烃。不对称方法的开发表明，1b 与 E 和 Z 异构体都反应，提供相同的绝对构型，而没有表现出 E-Z 异构化。这种立体收敛反应具有高产率（平均 86%）、高 S(N)2' 选择性（>99:1）和高 ee（平均 94%），并且使用纯 E 或 Z 异构体或 E/Z 烯烃混合物表现出广泛的官能团耐受性。立体收敛性特征使得可以使用许多不同的烯丙基化策略来生产底物，包括交叉复分解。手性烯丙基硼酸酯可以通过硅胶色谱法纯化，并储存在冰箱中而不会分解。
