One-pot ipso-hydroxylation and ortho-/para-halogenation of (hetero)arylboronic acids under tungsten catalysis

Abstract

A concise preparation of halophenols directly from (hetero)aryl boronic acids/esters via tungstate-catalyzed one-pot ipso-hydroxylation bromination and iodination has been developed in the current work. A broad substrate scope, good functional group tolerance and formal synthesis of several bioactive molecules have been achieved. Utilizing environmentally and costlyfriendly reagents (NaBr, NaI, H₂O₂, weak organic acids) and green solvents (EtOH/H₂O), this reaction can work at room temperature in the open air. It was also found to be dependent on pH, and to work smoothly with weak/moderate-strength organic acids without a tungsten catalyst. Compared to strategies developed in previous research with the same starting materials, this one-pot strategy was more step-economically friendly. Notably, the (hetero)aryl boronic acid played an interesting “one stone, two birds” role: as a starting material and promoter of the reaction by releasing B(OH)₃ as a co-catalyst. B(OH)₃ has normally been treated as waste in ipso-hydroxylation, but we expect the “turn waste into wealth (catalyst)” approach of the current work to inspire related research.