New chiral titanium complexes for enantioselective reductive cyclizations of diimines to trans-2,3-diarylpiperazines

Enantioselective intramolecular reductive coupling of diimines by chiral titanium complexes, prepared using a titanium(IV) reagent and hemisalen ligands derived from chiral β-amino alcohols, gives trans-2,3-diarylpiperazines in up to 97% ee.