Hydrochloride of chiral piperazine as a chiral proton source

Article abstract of DOI:10.1016/S0957-4166(00)82345-9

Asymmetric protonation utilizing hydrochlorides of chiral piperazine derivatives has been investigated. Protonation of the lithium enolate derived from 1-acetoxy-2-benzylcyclohexene with (2R,5R)-2,5-diphenylpiperazine monohydrochloride (2) resulted in a formation of (S)-2-benzylcyclohexanone in 70% ee. The enantioface-differentiating protonation with the salts of related chiral piperazine derivatives are also discussed.