Conversion of pinacol arylboronic esters 3 to aryl triolborates 5 via transesterification with 1,1,1-tris(hydroxymethyl)ethane (4) was established with the advantages of tolerance to various functional groups. Transesterification was carried out at 30-60 degrees C in dioxane in the presence of MOH (M = Na and K) and H2O. High yields were achieved for stable aryl triolborates 5.