Electroorganic chemistry. 129. Electroreductive synthesis of chiral piperazines and enantioselective addition of diethylzinc to aldehydes in the presence of the chiral piperazines
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.
A Simple Method of Synthesis of (±)-2,3-Diarylpiperazines and a Novel Method of Resolution of (±)-2,3-Diphenylpiperazine
作者:Pothiappan Vairaprakash、Mariappan Periasamy
DOI:10.1021/jo060083n
日期:2006.4.1
Intramolecular reductive coupling of diimines in the presence of Zn/Ti((OPr)-Pr-i)(2)Cl-2 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.