Use of Hemilabile N,N Ligands in Nitrogen-Directed Iridium-Catalyzed Borylations of Arenes

摘要

The direct activation of unreactive C—H bonds has emerged as a very active field in organic synthesis. One of the best established reactions in this area is the direct borylation of arenes with bis(pinacolato)diboron (B2pin2) or pinacolborane (HBpin). After the seminal work by Smith, Hartwig, Miyaura, and their respective co-workers, this method has reached an impressive level of chemical efficiency, mainly because of the introduction of the [Ir(μ-X)(cod)]2/di-tert-butylbipyridine (dtbpy; X = Cl, OMe; cod = 1,5-cyclooctadiene) precatalyst system. The regioselectivity of this reaction is typically driven by steric factors, thus making the method complementary to directed ortho-metalation (DoM) reactions. Very recently, however, directed ortho borylations have been accomplished by using directing groups such as siloxide or silylamine and carbonyl functionalities, but the absence of any nitrogen-directed borylation is noteworthy. Herein, we present our results on the regioselective ortho C—H borylation of 2-arylpyridines (isoquinolines) and aromatic hydrazones.