2014 年 72 巻 1 号 p. 26-38
Buckybowls are bowl-shaped aromatic hydrocarbons corresponding to a partial fullerene structure or a cap structure of carbon nanotubes. Since the discovery of C60 fullerene in 1985, buckybowls have attracted much attention due to their physical properties, not only as model compounds for fullerenes, but also as unique bowl-shaped aromatic compounds. We have achieved first enantioselective synthesis of chiral buckybowl, trimethylsumanene, and chiral azabuckybowl, triazasumanene. To achieve the synthesis, we have developed Pd-catalyzed syn-selective cyclotrimerization of enantiopure iodonorbornene derivatives, giving enantiopure C3 symmetric syn-tris(norborneno)benzenes. By using syn-tris(norborneno)benzene derivatives as synthetic intermediates, trimethylsumanene and triazasumanene were synthesized featuring tandem ring-opening/closing metathesis reaction or amide recombination reaction and oxidative aromatization. From the racemization experiments, the bowl inversion/racemization energies of trimethylsumanene and triazasumanene were determined to be 21.6 kcal/mol and 42.2 kcal/mol, respectively.