Electrochemical Transformations of Chiral Ni(II) Schiff Base Derivative of Serine: A Route to Novel Structures

Electrochemical oxidative functionalization of (R)‐ and (S)‐SerNi complexes performed in a biphasic H2O, NaBr, NaHCO3/CH2Cl2 system using TEMPO as a mediator results in the formation of a new glycine derivative brominated at the α‐amino acid carbon as well as at the para‐position of the aminophenylene ring in 70 % yield. The reaction is stereoselective; only the (S)‐diastereomer is formed, regardless of the stereo configuration of the starting complex, which can be either (S)‐ or (R)‐SerNi. The lability of the Cα‐−Cβ bond in SerNi precludes targeted oxidation of the hydroxy group in the carbonyl derivative even under the mild conditions. Meanwhile, a new dibrominated complex with a labile Cα‐Br bond (BDE is 27 kcal/mol) is a convenient precursor for further modification of the amino acid fragment, for example via nucleophilic reactions. The new α‐sulfanyl complex was obtained in 63 % yield. The mechanism of the electrochemical processes is discussed. SET point: TEMPO‐mediated electrooxidation of the Ni‐Schiff‐base derivative of serine opens a route to stereoselective preparation of a chiral equivalent of electrophilic glycine, which is a convenient precursor for further reactions with nucleophiles. Redox lability of the Cα‐Br bond (confirmed by the electrochemical data) creates a precondition for the single electron transfer (SET) follow‐up steps.