Iterative Reductive Aromatization/Ring-Closing Metathesis Strategy toward the Synthesis of Strained Aromatic Belts

The
construction of all sp2-hybridized molecular belts
has been an ongoing challenge in the chemistry community for decades.
Despite numerous attempts, these double-stranded macrocycles remain
outstanding synthetic challenges. Prior approaches have relied on
late-state oxidations and/or acid-catalyzed processes that have been
incapable of accessing the envisaged targets. Herein, we describe
the development of an iterative reductive aromatization/ring-closing
metathesis approach. Successful syntheses of nanohoop targets containing
benzo­[k]­tetraphene and dibenzo­[c,m]­pentaphene moieties not only provide proof of principle that
aromatic belts can be derived by this new strategy but also represent
some of the largest aromatic belt fragments reported to date.