N,N,N',N'-Tetramethylethylenediamine → (5-Chloro-1-benzofuran-2-yl)boronic acid

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Reaction Conditions

Reaction Steps

To a solution of 8.8 g (57.7 mmol) 5-chlorobenzofuran in 250 ml dry ether were added 7.32 g (63.0 mmol) tetramethylethylenediamine (TMEDA). The solution was kept below −60° C. under argon, while 37.5 ml of a 1.6M solution of butyllithium in hexane was added dropwise. It was warmed to −10° C. during 45 min and stirred at this temperature for another 30 min. The mixture was cooled again below −60° C. followed by dropwise addition of 35.7 g (190 mmol) triisopropyl borate. After warming to room temperature the mixture was quenched with 70 ml 2N hydrochloric acid and stirred for 1 h. The organic layer was washed three times with 30 ml 2N hydrochloric acid, twice with water, and extracted with 2N sodium hydroxide solution, successively. The alkaline aqueous layer was brought to pH5 and extracted with tert.-butylmethylether. All organic layers were combined, dried over sodium sulfate, and concentrated in vacuo to give the pale yellow crystalline boronic acid which was used for the next step without further purification.

Provenance & Evidence