Enantioselective alkylation of N-diphenylphosphinylimine with dialkylzincs using copolymerized chiral ligands

Enantioselective alkylation of N-diphenylphosphinylimine with dialkylzincs using monomeric chiral amino alcohols and copolymerized chiral amino alcohols as chiral ligands afforded N-diphenylphosphinylamines with high enantiomeric excess (EE). Among monomeric chiral ligands, N-vinylbenzylephedrine was the most highly enantioselective to afford the corresponding N-diphenylphosphinylamine with 95% EE. Chiral monomeric amino alcohols were copolymerized with styrene in the presence of crosslinking reagents such as divinylbenzene. The enantioselectivities of copolymerized chiral ligands were also high (up to 89% EE). Copolymerized chiral ligand was easily separated from the reaction mixture by filtration and was reused without considerable decrease in the enantioselectivity. Copolymerized chiral ligands prepared using crosslinking reagents with methylene spacers also showed high enantioselectivities, giving N-diphenylphosphinylamine with up to 90% EE. Regarding of the effect of solvent, aromatic hydrocarbons (toluene and benzene) and diethyl ether are appropriate. The effect of a spacer introduced on the nitrogen atom of the amino alcohol was also examined.