Sulfuric Acid → (2,5-Dimethylphenyl)boronic acid

Participants

Reaction Steps

Magnesium turnings (30.3 g; 0.55 mol) are placed ina baked-out apparatus flushed with argon, covered with about 30 ml of THF and treated with a few crystals of iodine. A few drops of bromo-p-xylene (cf. Example A1 a)) were subsequently added to the static solution. The Grignard reaction commenced very quickly and the remaining bromo-p-xylene (total amount: 92.5 g; about 70 ml; 0.5 mol) was subsequently added dropwise while stirring. The mixture was refluxed for 4 hours, then cooled. The Grignard solution was then transferred in a countercurrent of protective gas into a 500 ml dropping funnel and added dropwise at −70° C. to a solution of trimethyl borate (62.4 g; 67 ml; 0.6 mol) in 350 ml of THF while stirring (time: about 1 hour). During this addition, a precipitate was formed. The reaction mixture was allowed to warm to RT overnight and was then poured while stirring into a mixture of 700 g of ice and 20 ml of concentrated sulfuric acid. The organic phase was separated off, the aqueous phase was extracted three times with chloroform and the combined organic phases were evaporated. The crude product was recrystallized from chloroform/hexane.

Provenance & Evidence