1,3-Benzodioxole → 5-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-2H-1,3-benzodioxole

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To 25.1 mg PdCl2(dppf).CH2Cl2 in a reaction tube under nitrogen were added 4 ml dioxane, 0.42 ml (3 mmol) triethylamine, 0.16 ml (1.1 mmol) pinacolborane and 256 mg (1.03 mmol) 1-iodo-3,4-methylenedioxybenzene. The reaction solution was warmed to 80° C., with stirring, for 16 h in an oil bath. An aliquot (ca. 0.25 ml) of the reaction solution was removed, extracted into ethyl acetate and washed several times with water and brine solution and analysed by gc (fid detector, SGE HT5 capillary column). Hydrogen evolution was observed on the initial contact of the reaction sample with water, indicative that excess pinacolborane was present at the completion of the reaction even though only 1.1 equivalents had been used. Besides the 1,3-benzodioxole (10% of gc peak area) and pinacol ester of phenylboronic acid (7%), the only other product peak in the gc (area of 81%) was that due to the desired arylboronic acid pinacol ester. In a parallel reaction in which the only change was a reduction in the amount of triethylamine used, from 3.0 equivalents to 1.0 equivalents, the product distribution found was 1,3-benzodioxole (23% of gc peak area), the pinacol ester of phenylboronic acid (6%) and the desired arylboronic acid pinacol ester (peak area 69%).

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