Synthesis, Configurational Analysis, Molecular Recognition and Chirality Sensing of Methylene-Bridged Naphthotubes

Macrocyclic hosts with a well-defined cavity are particularly appealing for supramolecular chemistry, but they are still rare. In this research, we reported a new class of macrocyclic hosts, namely methylene-bridged naphthotubes, with well-defined cavities. They were synthesized through TFA-catalyzed Friedel-Crafts reactions between alkoxy-substituted bisnaphthalenes and paraformaldehyde. A configurational selection was observed. Three-membered macrocycles possess a single cavity, while four-membered macrocycles adopt a double-cavity conformation or a self-filling conformation depending on the alkoxy length. The small homologue shows quite strong binding affinities (up to 10⁸  M^-1 ) to organic cations, which is better than structurally similar but flexible macrocycles. This demonstrates the advantage of a well-defined cavity in molecular recognition. Moreover, these naphthotubes can be used as chirality sensors for chiral organic cations through different chirality transfer mechanisms.