Synthesis of novel chiral Ni~(II) complexes of dehydroalanine Schiff bases and their reactivity in asymmetric nucleophilic addition reactions. Novel synthesis of (S)-2-carboxypiperazine

摘要

New chiral Ni~(II) complexes of Schiff bases of dehydroalanine with modified chiral auxiliaries (S)-2-N-[N′-(3,4-dichlorobenzyl)prolyl] aminobenzophenone (3,4-DCBPB), (S)-2-N-[N′-(3,4-dimethylbenzyl)prolyl] aminobenzophenone (3,4-DMBPB), (S)-2-N-[N′-(2-chlorobenzyl)prolyl] aminobenzophenone (2-CBPB), and (S)-2-N-[N′-(2-fluorobenzyl)prolyl]- aminobenzophenone (2-FBPB) have been synthesized. Asymmetric Michael addition reactions of primary and secondary amines and thiols to the dehydroalanine moieties of the complexes were studied. (S)-2-FBPB was found to be the best chiral auxiliary in terms of both selectivity of the reactions (de ～92-96%) and reactivity of the complexes. A novel synthetic route toward (S)-2-carboxypiperazine was developed based on the auxiliary.