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/CH(2)Cl(2)system using TEMPO as a mediator results in the formation of a new glycine derivative brominated at the alpha-amino acid carbon as well as at thepara-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 C-alpha--C(beta)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 C-alpha-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 alpha-sulfanyl complex was obtained in 63 % yield. The mechanism of the electrochemical processes is discussed.