Electroorganic chemistry. 129. Electroreductive synthesis of chiral piperazines and enantioselective addition of diethylzinc to aldehydes in the presence of the chiral piperazines
摘要:
Electroreduction of diimines, prepared from 1,2-diamines and aromatic aldehydes, in acidic media gave intramolecularly coupled products, 2,3-diarylpiperazines, stereoselectively. Chiral tri- and tetrasubstituted piperazines were synthesized effectively from chiral 1,2-diamines by the same electroreductive method. Chiral piperazines, prepared from 1(R),2(R)-diaminocyclohexane were effective chiral ligands of catalysts for the enantioselective addition of diethylzinc to aldehydes.
The inter- and intramolecularcoupling of imines promoted by samariumdiiodide and Lewis acids or by Zn/MsOH was extensively studied. The intramolecularreaction of chiral, enantiomerically pure bis-imines was also considered, and allowed the efficient, stereoselective synthesis of 1,2-diamines with C2-symmetry.