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‐abstracting 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. DFT calculations suggest that an aromatic nucleophilic substitution is a key step in the formation of the products.