Asymmetric Transformation of α-Amino Acids Promoted by Optically Active Cobalt(III) Complexes. II. N-Methylalaninatocobalt(III) Complexes with Tetramines

Abstract The preparation and structural assignments of N-methyl-(S)- and -(R)-alaninatocobalt(III) complexes with a few chiral derivatives of 2,3,2-tet (=3,7-diazanonane-1,9-diamine) and triethylenetetramine are described. The hydroxide ion-catalyzed epimerizations of these complexes are examined at pH 10. In the N-methylalaninato complexes the isomer ratio for Λ-S/Λ-R ranged from 76/24 to 90/10. In the most favorable case where tetramine is 2(S)10(S)-4,8-diazaundecane-2,10-diamine (abbreviated as 2(S)10(S)-Me2-2,3,2-tet) the energy differences among the four possible diastereomers are discussed in relation to the prediction from strain energy minimization calculations.