Palladium-Catalyzed Cross-Coupling Reaction of Cyclopropylboronic Acids with Aryl Triflates
作者:Min-Liang Yao、Min-Zhi Deng
DOI:10.1055/s-2000-6313
日期:——
In the presence of appropriate base and NaBr, the Suzuki-type reaction of aryl triflates and trans-cyclopropylboronic acids proceed readily to give pure trans-cyclopropylarenes in good to high yields. For the reaction of general aryl triflates, the base KF · 2 H2O is efficient, but in the case of aryl triflates bearing electron donating groups, KF · 2 H2O as a base makes the unexpected phenyl-aryl exchange between the phenyl of Pd(PPh3)4 and the aryl of triflate to occur. The use of K3PO4 · 3 H2O instead of KF · 2 H2O can inhibit the unexpected phenyl-aryl exchange, but the yield of the product is somewhat decreased. The coupling reaction of aryl triflates with the optically active cyclopropylboronic acids, which were easily obtained in good yield and with good to excellent ee (up to 94%) by the asymmetric cyclopropanation of alkenylboronates with optically pure TMTA auxiliary, was also investigated. During the coupling reaction, the absolute configuration of the cyclopropyl group was retained. Thus, a novel method to prepare aryl-substituted cyclopropanes, including highly optically active cyclopropanes, from phenols or arylamines was provided.
在适当的碱和 NaBr 存在下,芳基三氟酸酯和反式环丙基硼酸的 Suzuki 型反应很容易进行,并以良好至高产率得到纯的反式环丙基烯烃。对于一般的芳基三氟酸酯反应,碱 KF - 2 H2O 是有效的,但对于带有电子捐赠基团的芳基三氟酸酯,KF - 2 H2O 作为碱会使 Pd(PPh3)4 的苯基和三氟酸酯的芳基之间发生意想不到的苯基-芳基交换。使用 K3PO4 - 3 H2O 代替 KF - 2 H2O 可以抑制意想不到的苯基-芳基交换,但生成物的产率会有所下降。通过烯基硼酸酯与光学纯 TMTA 助剂的不对称环丙烷化反应,可以轻松获得收率高、ee 值好到极好(高达 94%)的光学活性环丙基硼酸。在偶联反应过程中,环丙基的绝对构型得以保留。因此,提供了一种从苯酚或芳基胺制备芳基取代环丙烷(包括高光学活性环丙烷)的新方法。