Water soluble phosphines: Part XIII. Chiral phosphine ligands with amino acid moieties

Nucleophilic phosphination of the potassium or sodium salt of the fluorophenylalanines (1a, 2a) or -glycines (3a, 4a) with potassium phosphides Ph(R)PK (R=Me, Ph) yields chiral phosphine ligands (1–7) with amino acid moieties. The X-ray structure of 3·2H2O (space group Pbca) has been determined showing a betaine type structure for the amino acid moiety. The α-methyl derivatives of the phosphinophenylglycines (10, 11) were obtained in an analogous manner as 1–7. ortho- and para-Fluoroacetophenones have been employed as starting material for the syntheses of α-[4-fluorophenyl]-α-methylglycine (9c) and its ortho-isomer (8c), the X-ray structure of its monohydrate has been determined (space group P1̄). The N-acetyl (3b, 8e) and ester derivatives (3d, 8d) of 3 and 8c are accessible using standard procedures. Resolution of the diastereomeric salt 12 obtained from (S)-(+)-2-hydroxymethylpyrrolidine and racem-8e by fractionated crystallization yielded the (S,R)-isomer. The absolute configuration of (S,R)-12 was determined by X-ray structural analysis (space group P212121). Cleavage of (S,R)-12 with hydrochloric acid gave enantiopure (R)-8e [α]d20=−30.9° (c=1, CH3OH).