Denmark Scott E, Baird John D, Regens Christopher S
Department of Chemistry, University of Illinois Urbana-Champaign, Urbana, Illinois 61801, USA.
J Org Chem. 2008 Feb 15;73(4):1440-55. doi: 10.1021/jo7023784. Epub 2008 Jan 19.
The preparation of pi-rich 2-aryl heterocycles by palladium-catalyzed cross-coupling of sodium heteroarylsilanolates with aryl iodides, bromides, and chlorides is described. The cross-coupling process was developed through extensive optimization of the following key variables: (1) identification of stable, isolable alkali metal silanolates, (2) identification of conditions for preformation and isolation of silanolate salts, (3) judicious choice in the palladium catalyst/ligand combination, and (4) selection of the protecting group on the nitrogen of indole. It was found that the alkali metal silanolates, either isolated or formed in situ, offered a significant rate enhancement and broader substrate scope over the use of silanols activated by Brønsted bases such as NaOt-Bu. In addition, the optimized conditions for the cross-coupling of 2-indolylsilanolates were readily applied to the cross-coupling of 2-pyrrolyl-, 2-furyl-, and 2-thienylsilanolates.
描述了通过钯催化杂芳基硅醇钠与芳基碘化物、溴化物和氯化物的交叉偶联制备富π的2-芳基杂环化合物的方法。通过对以下关键变量进行广泛优化开发了交叉偶联过程:(1)确定稳定、可分离的碱金属硅醇盐;(2)确定硅醇盐盐的预形成和分离条件;(3)明智地选择钯催化剂/配体组合;(4)选择吲哚氮上的保护基。发现与使用由布朗斯台德碱(如叔丁醇钠)活化的硅醇相比,分离得到的或原位形成的碱金属硅醇盐能显著提高反应速率并拓宽底物范围。此外,2-吲哚基硅醇盐交叉偶联的优化条件很容易应用于2-吡咯基、2-呋喃基和2-噻吩基硅醇盐的交叉偶联。