Organoboron compounds. Part VIII. Aliphatic and aromatic diboronic acids

Abstract

Diboronic acids (HO)₂B·R·B(OH)₂(where R = polymethylene, arylene, or thiophen-2,5-diyl) are prepared by reactions of methyl borate with difunctional Grignard reagents and are characterised by the formation of cyclic esters with various diols. The polymethylenediboronic acids are much more resistant to aerial oxidation than are the corresponding alkylboronic acids. All the diboronic acids undergo dehydration to the corresponding polymeric anhydrides, the aromatic compounds requiring temperatures >230°. Reactions which result in deboronation or in the formation of amine complexes are described. Thiophen-2,5-diyldiboronic acid undergoes hydrogenolysis on treatment with Raney nickel to give tetramethylenediboronic acid.