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.).

同时兼具轴手性与平面手性的二茂铁类化合物的制备，长期以来都是极具挑战性的研究课题。在此，我们报道一种通过钯/手性降冰片烯（Pd/NBE*）协同催化，在二茂铁体系中同时构建轴手性与平面手性的策略。在该多米诺反应中，初始形成的轴手性由Pd/NBE*协同催化直接调控，而后续的平面手性则通过独特的轴-平面非对映诱导过程，由预先构筑的轴手性所控制。本方法以易得的邻二茂铁基取代芳基碘化物（共16个底物实例）与位阻较大的2,6-二取代芳基溴化物（共14个底物实例）作为起始原料。通过一步反应即可得到兼具轴手性与平面手性的5至7元环苯并稠合二茂铁类化合物（共32个产物实例），产物始终保持优异的对映选择性（>99% e.e.）与非对映选择性（>19:1 d.r.）。