(S)-3,3-Diphenyl-1-methylpyrrolidino[1,2-c]-1,3,2-oxazaborole

1. Convenient catalyst for the enantioselective borane reduction of ketones at ambient temperatures.
2. Asymmetric synthesis of α-chiral hydroxyalkylphosphines via a catalytic, enantioselective reduction of acylphosphines.
3. Nickel-catalyzed cross-couplings of benzylic pivalates with arylboroxines: Stereospecific formation of diarylalkanes and triarylmethanes.
4. Enantioselective reduction of prochiral ketones with NaBH4/Me2SO4/(S)-Me-CBS.

13061-96-6

22348-32-9

112022-81-8

Under nitrogen protection, (R)-(+)-α,α-diphenylprolinol (2.53 kg, 10 mol) and methylboronic acid (779 g, 13 mol) as well as 7.1 L of n-heptane were added to a reactor fitted with a reflux manifold. The mixture was stirred slowly and the solution gradually clarified as the water continued to separate. The stirring speed was then adjusted to conventional. When the water was completely separated, stirring was stopped and the reaction mixture was cooled to 40 °C and left to stand overnight. The reaction mixture was filtered through diatomaceous earth, and the filtrate was further cooled to -10°C and stirred for 1.5 hours to promote precipitation. The precipitate was collected by filtration and the product was vacuum dried in a double cone vacuum dryer at 40 °C for 8 h to give 2.30 kg (S)-2-methyl-CBS-oxazaborolidine in 83% yield. The product was a white solid with a GC purity of 98.2% and a water content of 0.31%.