Synthesis of the C₇₀ Fragment Buckybowl, Homosumanene, and Heterahomosumanenes via Ring-Expansion Reactions from Sumanenone

Bowl-shaped aromatic molecules, buckybowls, are attractive molecules because of the unique properties derived from their curved-π scaffolds. Doping heteroatoms into buckybowl frameworks is a powerful method to change their structural and electronical properties. Herein, we report the synthesis of C₇₀ fragment buckybowl, homosumanene, and heterahomosumanenes having a lactone moiety and a lactam moiety via three ring-expansion reactions using sumanenone as a common intermediate. X-ray diffraction analysis of the single crystals reveals their columnar packing structure with a shallow bowl-depth. The lactam moiety is readily derivatized to give azahomosumanene derivatives, nitrogen-doped analogues of homosumanene possessing a pyridine ring at the peripheral carbon. The synthetic application of the α-phenyl azahomosumanene as a cyclometalating ligand with platinum also revealed its utility for preparing a metal complex bearing a buckybowl ligand.