Room-Temperature Helix-to-Disc Conversion of Thia[6]helicene S,S-Dioxides to Coronene via In Situ Phenoxide Anion Generation.

Intramolecular annulation between the helical termini of helicenes provides a direct route to circulene-type architectures. In thia[6]helicene, oxidation at the thiophene terminus to the S,S-dioxide facilitates the thermal conversion to coronene, but established protocols typically require elevated temperatures. Herein, we demonstrate that forming a phenoxide anion at the benzene terminus of thia[6]helicene S,S-dioxides enables this transformation at room temperature, affording coronene in near-quantitative yield. Phenoxide arises either by deacetylation of the acetate precursor or by deprotonation of the corresponding phenol. Owing to the solubility contrast between the helical precursor and planar coronene, the product precipitates from solution, allowing the conversion to be monitored visually, and can be isolated by simple filtration. This helix-to-disc conversion begins with a stepwise intramolecular Diels-Alder reaction, and computational analysis elucidates the complete pathway to coronene. The present strategy delivers a practical room-temperature route to planar aromatic frameworks via an anion-triggered Diels-Alder reaction, without oxidative Scholl-type conditions, and broadens opportunities for the late-stage planarization of helicenes and related π-systems.