Hydrochloride of chiral piperazine as a chiral proton source

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