期刊
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
卷 56, 期 13, 页码 3712-3717出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.201611536
关键词
boranes; C-H activation; electrophilic substitution; homogeneous catalysis; Lewis acids
资金
- Alexander von Humboldt Foundation
In the electrophilic C-H borylation of electron-rich aromatic compounds with catecholborane, the catalytic generation of the boron electrophile is initiated by heterolysis of the B-H bond by various Lewis and Bronsted acids, with a boronium ion formed exclusively. After ligand dissociation, the corresponding borenium ion undergoes regioselective electrophilic aromatic substitution on aniline derivatives as well as nitrogen-containing heterocycles. The catalysis is optimized using B(C6F5)(3) as the initiator and proceeds without the addition of an external base or dihydrogen acceptor. Temperatures above 80 degrees C are generally required to secure efficient turnover in these Friedel-Crafts-type reactions. Mechanistic experiments reveal that regeneration of the boronium/borenium ion with dihydrogen release is rate-determining. This finding finally led to the discovery that, with added alkenes, catalytic C-H borylations can, for the first time, be carried out at room temperature.
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