已开发出一种用于将多种简单和杂环芳烃与芳基碘化物、溴化物和氯化物进行分子内直接芳基化的催化剂。这些反应以极好的收率发生并且具有高度选择性。对芳基碘化物底物的研究表明,由于碘化物在反应介质中的积累,会发生催化剂中毒。这可以通过添加银盐来克服,银盐也允许这些反应在较低温度下发生。该方法的效用通过咔唑天然产物的快速合成和通过直接芳基化产物的开环反应合成空间位阻四邻位取代的联芳基来说明。机理研究提供了对催化剂的深入了解 s 作用模式并显示在钯催化的简单芳烃的直接芳基化中存在动力学上显着的 CH 键裂解。从这些研究中获得的知识导致了以前无法获得的芳烃的新分子间芳基化反应的发展,为其他新的直接芳基化过程的发展打开了大门。
Aluminum Bases for the Highly Chemoselective Preparation of Aryl and Heteroaryl Aluminum Compounds
作者:Stefan H. Wunderlich、Paul Knochel
DOI:10.1002/anie.200804966
日期:2009.2.9
Selective CH activation with a series of neutral aluminum trisamide bases led to a wide range of polyfunctional aryl and heteroarylaluminum reagents. Ester and cyano groups are stable under the reaction conditions for this direct alumination, and donor oxygen substituents are efficient directing groups. High metalation regioselectivities were observed with O,S and N,S heterocycles (see example).
The directarylation of 1,3-benzodioxole and 2,2-difluorobenzo[1,3]dioxole with 26 different aryl bromides yields the respective 4-substitued products in yields of >80% requiring between 0.05–1 mol % Na2PdCl4, 30 mol % pivalicacid, 1.3 equivs. K2CO3 and ca. 250 equivs. of diethylacetamide per Pd at T=120 °C. The nature of the amide and the concentration of the reactants are crucial for the optimization