Synthesis, Characterization, and Study of Catalytic Activity of Chiral Cu Salen Complexes in the α-Amino Acid C-α Alkylation Reaction

• Published in: Molecules (Basel, Switzerland) Switzerland), 2023-01, Vol.28 (3)
• Main Authors: Tovmasyan, Anna S, Mkrtchyan, Anna F, Khachatryan, Hamlet N, Hayrapetyan, Mary V, Hakobyan, Robert M, Poghosyan, Artavazd S, Tsaturyan, Avetis H, Minasyan, Ela V, Maleev, Victor I, Larionov, Vladimir A, Ayvazyan, Armen G, Shibata, Norio, Roviello, Giovanni N, Saghyan, Ashot S
• Format: Article
• Language: English
• Subjects: Amino acids; Analysis; Catalysis; Evaluation; Properties; Schiff bases; Transition metal compounds
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28031180

A new family of Cu(II) and Ni(II) salen complexes was synthesized and fully characterized through various physicochemical methods. Their catalytic activity was evaluated in the phase transfer C[sub.α] -alkylation reaction of the Schiff bases of D,L-alanine ester and benzaldehyde derivatives. It was found that the introduction of a chlorine atom into the ortho- and para-positions of the phenyl ring of the substrate resulted in an increase in both the chemical yield and the asymmetric induction (ee 66–98%). The highest enantiomeric excess was achieved in the case of a Cu(II) salen complex based on (S,S)-cyclohexanediamine and salicylaldehyde at −20 °C. The occurrence of a bulky substituent in the ligand present in the complexes led to a drastic decrease in ee and chemical yield. For instance, the introduction of bulky substituents at positions 3 and 5 of the phenyl ring of the catalyst resulted in a complete loss of the stereoselectivity control in the alkylation reaction.