Iodine → (4-Propylphenyl)boronic acid

Participants

Reaction Steps

To a suspension of magnesium shavings (21 7 mg, 8.9 mmol) in 3 mL of dry tetrahydrofuran under argon, a crystal of iodine along with a solution of 4-bromopropylbenzene (1.69 g, 8.5 mmol) dissolved in 6 mL of tetrahydrofuran was added at such a rate that a gentle reflux was maintained. The solution was refluxed for an additional 0.5 h, cooled to room temperature and added in portions over 10 min to a solution of trimethylborate (924 mg, 8.9 mmol) previously dissolved in 4 mL of dry ether at -78° C. After 30 minutes, the solution was warmed to room temperature; and stirring was continued for 90 min. The reaction was then quenched by the addition of 2 mL of a 10% hydrochloric acid solution. The tetrahydrofuran was removed under reduced pressure and the remaining residue was extracted into diethyl ether (3×25 mL). The combined ether extracts was extracted with 1M NaOH (3×25 mL) and the resulting aqueous layer was acidified to pH 2.0 using 6N HCl, then reextracted back into diethyl ether (3×25 mL). The combined organic layers was washed with water (1×25 mL), brine (1×25 mL) and dried over magnesium sulfate. Evaporation of solvent left a brown solid which was filtered through a small plug of silica gel using 10% MeOH/CHCl3. Evaporation left 448 mg (32%) of a brown solid, m.p. 90°-93° C.

Provenance & Evidence