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

Trimethylsilyl-protected tetrafluorinated thia[6]helicene S-oxide undergoes a more efficient transformation to difluorinated coronene than its unprotected S-oxide and S,S-dioxide counterparts. Si···F interactions and in-situ-generated sulfur monoxide facilitate selective desilylation, offering mechanistic insight into this cascade transformation.

Abstract

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.

Zum Volltext