Trimethyl borate → Dimethyl 2-(2-dimethylaminoethyl)benzeneboronate

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19.0 g (83.2 mmol) of the [2-(2-bromophenyl)ethyl]dimethylamine prepared according to example 10 (2nd stage) were dissolved in 300 ml tetrahydrofuran and the solution was cooled to −70° C. in a cooling bath (isopropanol/dry ice). 60 ml (95.7 mmol) butyllithium solution (1.6 M in hexane) were added dropwise under nitrogen such that the temperature did not rise above −60° C. After the mixture had been stirred at −70° C. for two hours, 28 ml (250 mmol) trimethyl borate were also added dropwise such that the temperature did not rise above −60° C. The mixture was warmed to 25° C. in the course of 15 hours and the solution was concentrated on a rotary evaporator (500-10 mbar) without heat being supplied. The residue was taken up in 200 ml n-hexane, the mixture was stirred for one hour and filtered over an inert gas frit under nitrogen and the filtrated was concentrated on a rotary evaporator (500-10 mbar) without heat being supplied. 14.1 g dimethyl 2-(2-dimethylaminoethyl)benzeneboronate (76.5% of theory) were obtained in this manner.

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