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 sp 2 C-H of arene is activated and both boryl units are utilized to build two new (sp 2 )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.