A Simple Method of Synthesis of (±)-2,3-Diarylpiperazines and a Novel Method of Resolution of (±)-2,3-Diphenylpiperazine

Intramolecular reductive coupling of diimines in the presence
of Zn/Ti(OiPr)2Cl2 gives the corresponding (±)-2,3-diarylpiperazines in 73−83% yields with dl/meso ratio >99%:<1%. The (±)-2,3-diphenylpiperazine obtained in this way
was readily resolved partially using l-(+)-tartaric acid, and
the enantiomeric purity was enhanced to >99% ee via
preparation of hydrogen-bonded salt aggregates using oxalic
acid.