1,1-Dibromoethane → 1-(N,N-diethylamino)-2,5-dimethylborolane

Beteiligte Stoffe

Reaktionsbedingungen

Reaktionsschritte

Dibromoethane (3.0 mL, 0.035 mol) was added to a mechanically stirred suspension of Mg turnings (78 g, 3.21 mol) in THF (160 mL). After 30 min. most of the THF was removed via cannula and fresh THF (270 mL) was added. Then a solution of 2,5-dibromohexane (299 g, 1.24 mol) in THF (650 mL) was added at a rate that maintained the internal temperature at 30°-34° C. The resulting mixture was stirred overnight, filtered through glass wool and diluted with THF to a volume of 2 L. Hydrolysis of an aliquot and titration for total base showed the concentration of this solution to be 0.39M (63% yield, typically 60-65%). The Grignard solution was added to a cooled, magnetically stirred solution of N,N-diethylaminodichloroborane (124 g, 0.80 mol) in ether (1.0 L) at a rate that allowed maintenance of an internal temperature of -70° to -65° C. The resulting suspension was allowed to warm to 20° C. overnight. The solids were allowed to settle and the supernatant was removed via cannula. The solids were washed with pentane (four times) and the combined supernatants were concentrated by fractional distillation. The residue was vacuum transferred to a cold (dry ice-acetone) receiver by heating the residue to 120° C. at 0.1 torr. Distillation under reduced pressure gave the diethylaminoborolane 7 as a mixture of isomers (72.8 g, 0.44 mol) in 56% yield. On a small scale yields up to 70% were obtained.

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