The general procedure for the synthesis of 2-cyanophenylboronic acid-1,3-propanediol cyclic ester from 2-cyanophenylboronic acid and 1,3-propanediol is as follows: 3.69 g (48.5 mmol) of 1,3-propanediol was added to the organic phase obtained from Example 1 and the reaction mixture was stirred for 1 hour at room temperature. Upon completion of the reaction, the aqueous phase was separated and removed, followed by distillation using a rotary evaporator to remove the organic solvent. To the residual oily substance, 2 ml of toluene and 120 ml of heptane were added to induce crystallization. The resulting crystals were washed with 30 mL of heptane and 7.44 g (yield: 82.4%) of the target product 1,3-propanediol ester (2-(1,3,2-dioxaborolan-2-yl)benzonitrile) was obtained after drying. The crystals were analyzed to contain 0.40% impurity of 1-phenyl-1-(2,2,6,6-tetramethylpiperidin-1-yl)methanimine.
