Diboronic Acid Usable for the Direct Synthesis of Aromatic Boric Acid Derivatives

Tetrahydroxydiborane (1) is a useful boric acids group-introducing reagent and is used for the synthesis of aromatic boric acid derivatives.^1-5） For instance, 1 successfully reacts with aryl chlorides under the conditions of Palladium-XPhos ligands-catalytic systems to afford the desired aryl boric acids. After the borylations, their diesters or trifluoroborates are further obtained by the esterification with some diols or the treatment with KHF₂ respectively.^1-3） For other catalytic systems to perform this reaction, nickel-catalyzed aryl borylations have been developed.⁴⁾ Recently, transition-metal-free aryl borylations have been reported. This easy aryl borylation proceeds via the aryl diazonium salt intermediates formed from aromatic amines.^5）