Efficient system for facile access to ortho-substituted aryl boronates through palladium-catalysed borylation

A study on the effects of ligand steric bulk in the Pd-catalysed borylation of ortho-substituted aryl bromides and chlorides under mild conditions (25 – 80 °C) is described. Catalysts derived from the less hindered biaryl phobane[3.3.1] 1 (cone angle = 178.5°) have demonstrated high efficiency for borylation of a wide array of ortho-substituted aryl bromides. Dialkylbiaryl phosphine 5 (cone angle = 181.3°) and biaryl phosphacycle 2 (cone angle = 220.0°) exhibited suitable ligand steric bulk for facile Pd-catalysed borylation of ortho-substituted aryl chlorides.