Trimethyl borate → (4-Propylphenyl)boronic acid

To a suspension of magnesium shavings (217 mg, 8.9 mmol) in 3 mL of dry tetrahydrofuran under argon, a crystal 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 minutes 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 where stirring continued for 90 minutes, then the reaction was 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 11.0 MeOH/CACl3. Evaporation left 448 mg (32%) of a brown solid, m.p. 90°-93° C.

1. additionwas added at such a rate that
2. temperaturea gentle reflux
3. temperaturewas maintained
4. temperatureThe solution was refluxed for an additional 0.5 h
5. temperaturethe solution was warmed to room temperature where
6. waitcontinued for 90 minutes
7. customthe reaction was quenched by the addition of 2 mL of a 10% hydrochloric acid solution
8. customThe tetrahydrofuran was removed under reduced pressure
9. extractionthe remaining residue was extracted into diethyl ether (3×25 mL)
10. extractionThe combined ether extracts was extracted with 1M NaOH (3×25 mL)
11. washThe combined organic layers was washed with water (1×25 mL), brine (1×25 mL)
12. dry with materialdried over magnesium sulfate
13. customEvaporation of solvent
14. waitleft a brown solid which
15. filtrationwas filtered through a small plug of silica gel using 11.0 MeOH/CACl3
16. customEvaporation
17. waitleft 448 mg (32%) of a brown solid, m.p. 90°-93° C.

ORD record

ord-0ab25967fefe4222baea8fd19d8f08e7

Source dataset

uspto-grants-1996_11

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US05571821