Tetrabutoxy-substituted quintulene: A missing bowl-shaped cycloarene.

The synthesis of corannulene and sumanene has pioneered the burgeoning field of buckybowl chemistry. Quintulene, a long-missing member of cycloarenes family, represents a distinctive type of bowl-shaped aromatics with curvature arising from edge topology and central cavity. Nevertheless, its synthesis has remained elusive for more than 40 years, primarily due to the high geometric strain. Herein we report the synthesis of tetrabutoxy-subtituted quintulene 1 through a rationally designed fold-in strategy. Single crystal analysis confirms the bowl-shaped geometry with a bowl-to-bowl inversion barrier of 19.1 kcal/mol. Quintulene 1 adopts a Clar-type localized aromatic character, consistent with other cycloarenes, but prone to hydrogenation and over-oxidation. Remarkably, the substantially structural strain attenuates local aromaticity in the benzenoid segments of quintulene 1, enabling an almost quantitative fivefold Diels-Alder reaction. This work not only fills a critical gap in cycloarene chemistry but also underscores how geometric strain and electronic structure can reshape reactivity in curved π-systems.