title: Catalytic Friedel-Crafts C-H Borylation of Electron-Rich Arenes: Dramatic Rate Acceleration by Added Alkenes.
abstract: 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 Brønsted 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)3as the initiator and proceeds without the addition of an external base or dihydrogen acceptor. Temperatures above 80 °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.
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 115, 10623, Berlin, Germany.
authors.forename: Qin
authors.identifier: 0000-0003-3534-3786
authors.initials: Q
authors.lastname: Yin
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 115, 10623, Berlin, Germany.
authors.forename: Hendrik F T
authors.identifier: 0000-0003-3748-6609
authors.initials: HF
authors.lastname: Klare
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 115, 10623, Berlin, Germany.
authors.forename: Martin
authors.identifier: 0000-0002-1487-9218
authors.initials: M
authors.lastname: Oestreich
keywords: C−H activation; Lewis acids; boranes; electrophilic substitution; homogeneous catalysis