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

The construction of all sp(2)-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.