Transformation of Silyl-Protected Tetrafluorinated Thia[6]helicene S-Oxide into a Difluorinated Coronene via Induced...

Sulfur oxidation of thiophene rings is an effective strategy for constructing substituted and polycyclic arenes via Diels-Alder reactions, wherein each thiophene ring is converted into a benzene ring. In the context of converting helicenes into planar coronenes, tetrafluorinated thia[6]helicene S,S-dioxide undergoes a smooth intramolecular Diels-Alder reaction to afford the difluorinated coronene. However, the corresponding S-oxide counterpart is affected by competing side reactions that limit its utility. Herein, we demonstrate that introducing a trimethylsilyl (TMS) group onto the thiophene S-oxide ring suppresses self-condensation and enables more efficient coronene conversion than its S,S-dioxide counterpart. Unexpectedly, the TMS group is removed during the transformation, yielding both the TMS-protected and deprotected forms of the difluorinated coronene. Mechanistic investigations suggest that this desilylation arises from the combined effect of Si···F interactions and in-situ-generated sulfur monoxide (SO). These findings provide insights into the reactivity control of thiophene S-oxides and demonstrate how silicon, fluorine, and SO can influence cascade transformations toward functionalized polycyclic aromatic systems.