Titanium-Catalyzed C─X and C─H Borylation of Aryl Halides for the Synthesis of Bis(boronate)benzenes.

Despite the intensive studies on the synthesis and application of aryl boronates, most focus on mono-borylated arenes. The multi-borylated arenes, on the other hand, have received much less attention because the preparation of multi-borylated arenes in a straightforward manner is still underdeveloped. Herein, we present our findings on synthesizing bis-borylated arenes from structure-diverse and readily available aryl halides (Ar─X, X = Cl, Br, I). Simultaneous C─X and C─H borylation of aryl halides is achieved using earth-abundant titanium as a catalyst. Not only the 1,2-bis borylation but also the 1,3- and 1,4-bis borylation are achieved. Control experiments and density functional theory (DFT) computations propose a titanium-mediated aryl radical-driven reaction resulting in selective bis-borylation over mono-borylation.