Stereoselective synthesis of [2.2]triphenylenophanes via intramolecular double [2 + 2 + 2] cycloadditions

Abstract

Planar chiral [2.2]cyclophanes with two aromatic rings in close proximity have attracted much attention for their applications as chiral materials and catalysts because of their stable chirality and transannular interactions. Although numerous [2.2]cyclophanes have been synthesized to date, only a few polycyclic aromatic hydrocarbon (PAH)-based ones have been reported, and the simultaneous control of two planar chiralities of the two aromatic rings facing each other has not been achieved. Here we report the enantio- and/or diastereoselective synthesis of planar chiral PAH-based [2.2]cyclophanes ([2.2]triphenylenophanes) via the high-yielding base-mediated intermolecular macrocyclization and Rh- or Ni-catalyzed intramolecular double [2 + 2 + 2] cycloadditions. DFT calculations have revealed that the second [2 + 2 + 2] cycloaddition kinetically determines the diastereoselectivity. Single crystal X-ray diffraction analyses have confirmed that the facing triphenylene or [5]helicene skeletons strongly repel each other, resulting in curved structures with bulged centers.