Synthesis
A dry three-neck flask equipped with a rubber septum, an addition funnel equipped with a rubber septum, and a condenser was charged under nitrogen with magnesium turnings. To the addition funnel was added D5-bromobenzene (6.5 mL, 62 mmol) (Aldrich) dissolved in a 1:1 mixture of THF/toluene (31 mL). Grignard reagent formation was observed after about after about 1 mL of the contents of the addition funnel had been added to the magnesium turnings. The remaining bromobenzene solution was added dropwise over a period of about 1 h. After the addition was complete the reaction mixture was heated at 70° C. for 1 h. The reaction mixture was cooled to room temperature and added via a canulating needled to an addition funnel on a second three-neck flask containing a solution of triethylborate (B(OEt)3) (10.5 mL, 62 mmol) in toluene (10 mL) maintained at 0° C. The solution of the freshly prepared Grignard reagent was then added dropwise to the solution of triethylborate over a period of 1 h. The cooling bath was then removed and the reaction mixture was allowed to stir at room temperature for 15 h. The reaction mixture was quenched with 10% H2SO4 (30 mL) and stirred at room temperature for 1 h. The layers were separated and the organic layer was dried over Na2SO4. After removal of the solvent, addition of hexane precipitated the product as an off-white solid, which was collected by filtration and dried to afford Phenyl-d5-boronic acid. Its yield: 3.50 g, 45%.
