Diastereomeric amides from rac-3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxylic acid and (S)-α-phenylethylamine: separation and determination of absolute configuration

Reaction of racemic 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxylic acid 1 with (S)-α-phenylethylamine in the presence of benzotriazol-1-yl-oxytris-(dimethylamino)phosphonium hexafluorophosphate and diisopropylethylamine leads to diastereomeric amides, (S,R)-2 and (S,S)-2. The diastereomers were separated by column chromatography and their absolute configurations were determined from NMR data supported by molecular modeling.