Stereoselective Synthesis of α-Amino(phenyl)methyl(phenyl)phosphinic Acids with O-Pivaloylated D-Galactosylamine as Chiral Auxiliary

Stereoselective synthesis of α-amino (phenyl)methyl(phenyl)phosphinic acids with O-pivaloylated D-galactosylamine as chiral auxiliary, was reported. 2 3 drops of acetic acid were added to a solution of amine 1 and aldehyde 2 in 2-propanol and the mixture was stirred at room temperature for about 0.5 h. A solution of N-galactosylaldimines 3 in THF was cooled to 0°C, and phosphinate 4 and SnCl4 were added. The mixture was stirred for 2 d at room temperature. The aqueous phase was extracted with CHCl3 and the organic layers were dried with anhydrous MgSO4, filtered, and concentrated in vacuo to yield the crude products. A solution of compound 5 in dry methanol was treated with freshly prepared solution of HCl. Then methanol was evaporated in vacuo and the remaining residue dissolved in 0.5 M HCl and extracted with pentane. The results revealed that AlCl3, SnCl 4, and BF3.OEt2 were able to promote the addition.