UNUSUAL AMINO-ACIDS .7. ASYMMETRIC-SYNTHESIS OF 3-PYRIDYLALANINES AND4-PYRIDYLALANINES

(Z)-2-N-Acylamino-3-pyridyl-acrylic acids and their esters were prepar ed by partially known procedures and hydrogenated in the presence of H BF4 to the corresponding optically active 2-N-acetyl-(or benzoyl-)-3-( 3- or 4-pyridyl)-alanines or analogous methyl esters with enantiomeric excesses up to 90%. The rhodium complexes of PROPRAPHOS, 6a,b, or of O,N-bis(diphenylphosphino)-2-exo-hydroxy, 3-endo-methylamino-norbor-na ne, 6c, as chiral catalysts have been used in the presence ol HBF4 to generate the corresponding pyridinium salts. Deacylation of the recrys tallized amino acid derivatives or further recrystallization of the fr ee amino acids yielded enantiomerically pure D- and L-pyridylalanines.