N-benzyl-L-prolinol:: an efficient catalyst for the enantioselective addition of dialkylzinc reagents to N-(diphenylphosphinoyl)imines

Commercially available N-benzyl-L-prolinol has shown to be a very efficient catalyst for the enantioselective addition of dialkylzinc reagents to N-(diphenylphosphinoyl)imines. The use of 0.5 equiv of this beta-aminoalcohol as a catalyst leads to the expected addition products in good yields and with ees up to 92% in a reaction time of only 4 h at room temperature. This ee is almost equal to the highest value reported so far using 0.5 equiv of an aminoalcohol as promoter, although the reaction time is much shorter in our case. The amount of the catalyst can be reduced to 0.25 equiv with a slight decrease in the ee. An interesting effect of the addition rate and temperature on the enantioselectivity has been observed. (c) 2007 Elsevier Ltd. All rights reserved.