Stereoselective Pinacol Coupling of Planar Chiral (arene) chromium Complexes ; Synthesis of Optically Pure 1,2-Dihetero Compounds

点击翻译按钮获取中文摘要

Enantiomerically pure 1, 2-diols and diamines are important compounds as chiral ligand or auxiliary in asymmetric reaction. The reductive coupling of carbonyl compounds, pinacol coupling, is the most direct way to synthesize 1, 2-diols. Although this reaction can be achieved in high yield by lanthanoid metals or low valent transition metals, highly stereoselective formation of 1, 2-diols is problematic under conventional reductive coupling methods. (Arene)chromium complex can exist in two enantiomeric forms based on the planar chirality. We have investigated the pinacol coupling of planar chiral chromium complexes of benzaldehydes and benzaldiminesEnantiomerically pure (o-substituted benzaldehyde)Cr(CO)_3 complexes and (o-substituted benzaldimine)Cr(CO)_3 complexes were treated with samarium diiodide in THF to produce stereoselectively optically pure chromium-complexed threo-diols and diamines, respectively. These chromium-complexed threo-diols and diamines were oxidized to give the chromium free 1, 2-diols and diamines in enantiomerically pure form. Similarly, planar chiral (diene)Fe(CO)_3 and alpha-substituted ferrocencarboxaldehydes produced the corresponding enantiomerically pure 1, 2-diols in high yield.Furthermore, an intramolecular pinacol coupling of enantiomerically pure chromium complexes of axially chiral biphenyls having dicarbonyl, diimine and iminokarbonyl function afforded to trans 1,2-diols, diamines and aminoalcohols, respectively, under the same reaction conditions.