Catalyst‐Free Regioselective Diborylation of Aryllithium with Tetra(o‐tolyl)diborane(4)

A catalyst‐free 1,2‐diborylation of aryllithium with tetra(o‐tolyl)diborane(4) has been achieved, giving a series of 1,2‐diborylaryl lithium species in excellent yields under mild reaction conditions, which leads to 1,2‐di(tolyl)borylarenes in 60–91 % yields upon treatment with the hydride‐ing reagent. In these transformations, one sp2 C−H of arene is activated and both boryl units are utilized to build two new (sp2)C−B bonds. This represents a new strategy for selective arene diborylation. Density functional theory (DFT) calculations suggest that an aromatic nucleophilic substitution is a key step in the formation of the products. A catalyst‐free highly regioselective and efficient o‐diborylation of aryllithium with tetra(o‐tolyl)diborane(4) has been developed, leading to a family of o‐diborylarenes in very good yields under mild reaction conditions. Density functional theory calculations reveal that an aromatic nucleophilic C(sp2)−H substitution pathway may be involved.