Phenanthrylene–alkynylene macrocycles, phenanthrene-fused dicyclopenta[b,g]naphthalene, as well as relevant diradicaloids and antiaromatic compounds

Abstract

Abstract Antiaromaticity and diradical character are fundamentally important interrelated concepts in π-conjugated systems. Both antiaromatic compounds and open-shell singlet diradicaloids are generally unstable; however, over the past decade, the physical organic chemistry of antiaromatic compounds and diradicaloids has seen significant development following pioneering studies on the synthesis of stable examples. This chapter mainly summarizes the structure–π-conjugative property relationships of antiaromatic compounds and diradicaloids, namely, (i) tetralkoxyphenanthrene-fused octadehydro[12]annulenes, (ii) benzo- and naphthopentalenes, (iii) phenanthrene-fused dicyclopenta[b, g]naphthalene and its congeners, as well as (iv) difluoreno[4,3-b:3′,4′-d]furan, which was synthesized in the author's research group. Insights into the π-stacking interactions of (v) tetraalkoxyphenanthrylene–alkynylene macrocycles with extended polyyne chains are also described.