Asymmetric synthesis of S-alkyl-substituted (R)-cysteines via a chiral NiII complex of the Schiff's base of dehydroalanine with (S)-2-N-(N-benzylprolyl)aminobenzophenone

Article abstract of DOI:10.1007/BF02495097

An efficient procedure was developed for the asymmetric synthesis of S-alkyl derivatives of (R)-cysteine by nucleophilic addition of alkanethiols (BuⁿSH, Bu^tSH, or tert-C₅H₁₁SH) to the C=C bond of the dehydroalanine fragment in the Ni¹¹ complex of the Schiff's base of Δ-Ala with (S)-2-N-(N-benzylprolyl)aminobenzophenone [(S)-BPB-Δ-Ala]Ni¹¹. Under conditions of thermodynamic control of the reaction, the diastereomeric excess of the complexes with the (S,R)-configuration was 88 - 96%. After decomposition of the complexes, (R)-S-butylcysteine, (R)-S-tert-butylcysteine, and (R)-S-tert-pentylcysteine were isolated with an enantiomeric purity of >97%.