Enantioselective Assembly of Ferrocenes with Axial and Planar Chiralities via Palladium/Chiral Norbornene Cooperative Catalysis

The preparation of ferrocenes with both axial and planar chiralities poses a considerable challenge. Herein, we report a strategy for the construction of both axial and planar chiralities in a ferrocene system via palladium/chiral norbornene (Pd/NBE*) cooperative catalysis. In this domino reaction, the first established axial chirality is dictated by Pd/NBE* cooperative catalysis, while the latter planar chirality is controlled by the preinstalled axial chirality through a unique axial-to-planar diastereoinduction process. This method exploits readily available ortho-ferrocene-tethered aryl iodides (16 examples) and the bulky 2,6-disubstituted aryl bromides (14 examples) as the starting materials. Five- to seven-membered benzo-fused ferrocenes with both axial and planar chiralities (32 examples) are obtained in one step with constantly high enantioselectivities (>99% e.e.) and diastereoselectivities (>19:1 d.r.).同时兼具轴手性（axial chirality）与平面手性（planar chirality）的二茂铁（ferrocenes）的合成极具挑战性。本文报道了一种通过钯/手性降冰片烯（palladium/chiral norbornene, Pd/NBE*）协同催化，在二茂铁体系中同时构筑轴手性与平面手性的策略。在该多米诺反应（domino reaction）中，首先构筑的轴手性由Pd/NBE*协同催化决定，而后续生成的平面手性则通过独特的轴-平面非对映诱导过程，由预先引入的轴手性进行调控。该方法以易于获取的邻二茂铁基芳基碘化物（共16个反应实例）与大位阻2,6-二取代芳基溴化物（共14个反应实例）作为起始原料。一步即可得到兼具轴手性与平面手性的5至7元苯并稠合二茂铁（benzo-fused ferrocenes）类化合物（共32个反应实例），产物始终保持优异的对映选择性（对映体过量百分比>99% e.e.）与非对映选择性（非对映体比例>19:1 d.r.）。