Reductive Asymmetric Cross Pinacol Coupling Utilizing Planar Chiral Transition Metal Complexes

对映体纯的β-二醇、二胺和氨基醇已被广泛用作手性配体或不对称反应的助剂，并且在生物活性天然产物的关键合成中间体中也很重要。虽然光学纯的β-二醇可以通过烯烃的催化不对称二羟基化反应方便地制备，具有高的光学纯度，但制备手性二胺的普遍接受的方法涉及用某些手性羧酸对外消旋化合物进行光学拆分。羰基或亚胺化合物的还原偶联，即高频哪醇偶联，是制备b-二醇或二胺的最直接方法。虽然该反应可以通过镧系金属或低价过渡金属以高产率实现，但是在常规还原偶联下高度非对映选择性地形成b-二醇或二胺是有问题的。我们成功地利用碘化钐介导的N-对甲苯磺酰基二茂铁亚甲基胺与平面手性二茂铁甲醛或苯甲醛铬配合物的交叉偶联反应，通过与平面手性芳醛的偶联反应，非对映选择性地合成了相应的反式β-氨基醇。研究了碘化钐还原非手性N-对甲苯磺酰基二茂铁胺和亚苄基胺生成的构型平衡反应物种与平面手性芳醛的交叉偶联动力学拆分，根据平面手性，得到β-氨基醇的两个对映体。以所合成的反式β-氨基二茂铁为配体，催化苯乙酮的不对称还原反应。

Enantiomerically pure β-diols, diamines, and amino alcohols have found widespread use as chiral ligands or auxiliaries as asymmetric reactions, and are also important in key synthetic intermediates for biologically active natural products. While optically pure b-diols have been conveniently prepared by catalytic aymetric dihydroxylation of the olefins with high optical purity, the generally accepted method for the preparation of chiral diamines involvesan optical resolution of racemic compounds with certain chiral carboxylic acids. A reductive coupling of carbonyl or imine compounds, homo-pinacol coupling, is the most direct method for the preparation of b-diols or diamine. Although this reaction can be achieved in high yield by lanthanoid metals or low valent transition metals, highly diastereoselective formation of b-diols or diamines is problematic under conventional reductive coupling. We have succeeded that samarium idode-mediated cross-coupling of N-tosyl ferrocenylideneamine with planar chiral ferrocenecarboxaldehydes or benzaldehyde chromium complexes gave diastereoselectively the corresponding anti-β-amino alcohols by coupling with planar chiral arylaldehydes. Dynamic kinetic resolution of a configurationally equilibrated reactive species generated from achiral N-tosyl ferrocenilideneamine and benzylideneamine by reduction with samarium iodide was observed in the cross-coupling with planar chiral arylaldehydes giving both antipodes of β-amino alcohols depending on thee planar chirality. The obtained anti-β-amino with the ferrocene ring was utilized as a ligand for catalytic asymmetric reduction of acetophenone.