Enantioselective alkylation of N-diphenylphosphinylimine with dialkylzincsusing copolymerized chiral ligands

Enantioselective alkylation of N-diphenylphosphinylimine with dialkylzincs using monomeric chiral amino alcohols and copolymerized chiral amino alcoho ls as chiral ligands afforded N-diphenylphosphinylamines with high enantiom eric excess (EE). Among monomeric chiral ligands, N-vinylbenzylephedrine wa s the most highly enantioselective to afford the corresponding N-diphenylph osphinylamine with 95% EE. Chiral monomeric amino alcohols were copolymeriz ed with styrene in the presence of crosslinking reagents such as divinylben zene. The enantioselectivities of copolymerized chiral ligands were also hi gh (up to 89% EE). Copolymerized chiral ligand was easily separated from th e reaction mixture by filtration and was reused without considerable decrea se in the enantioselectivity. Copolymerized chiral ligands prepared using c rosslinking reagents with methylene spacers also showed high enantioselecti vities, giving N-diphenylphosphinylamine with up to 90% EE. Regarding of th e effect of solvent, aromatic hydrocarbons (toluene and benzene) and diethy l ether are appropriate. The effect of a spacer introduced on the nitrogen atom of the amino alcohol was also examined. (C) 1999 John Wiley & Sons, Lt d.