1998 Volume 56 Issue 8 Pages 672-680
Widespread use of homochiral 1, 2-diary1-1, 2-diaminoethanes and 2-amino-1, 2-diarylethanols as chiral auxiliaries coupled with difficulties associated with their preparation prompted us to investigate new methodologies for their syntheses. For the preparation of this highly useful class of compounds, enantioselective imino pinacol coupling of p-anisylbenzal-imine was investigated using Zn-Cu couple in the presence of (+) -camphorsulfonic acid as a chiral auxiliary to give (R, R) -1, 2-diphenylethylenediamine derivative in high enantiomeric purity. Highly enantioselective reduction of 1, 2-bis (p-methoxyphenylimino) -1, 2-diphenylethane was also conducted with 0.5 mol% of the new oxazaborolidine, derived from L-threonine and a stoichiometric amount of BH3· THF, to give 1, 2-diphenylethylenediamine derivative in excellent enantiomeric purity. The subsequent deprotection of nitrogen atoms afforded (R, R) -1, 2-diphenylethylenediamine in enantiomerically pure form. Moreover, the reduction of 1, 2-diaryl-2-benzyloxyiminoethanones conducted using the above oxazaborolidine and BH3 ·SMe2 gave β-imino alcohols chemoselectively in high enantiomeric purity. Subsequent selective reduction of the imino functionality affords either syn- or anti-2-amino-1, 2-diarylethanols in high enantiomeric purity by choosing appropriate reduction conditions.
