Catalytic Dearomative [1,5]‐Sigmatropic Carbon Shift of Heterole‐Fused Norcaradienes Enabled Concise Helicenation

In contrast to the locked fluxionality of norcaradienes fused by benzene, unexplored less aromatic heterole‐fused norcaradienes, creatively generated by intramolecular hydroarylation of heteroaryl alkynylcyclopropanes, reserve a balancing fluxionality that permits a dearomative [1,5]‐sigmatropic carbon shift of norcaradienes akin to the reduced aromaticity of heterole. This “walk” shift was confirmed by the isolation of a cycloheptatriene species derived from ring‐expansion of a dearomatized alkynylated heterole‐fused norcaradiene. A following ester‐directed ring‐opening rearomatization of these dearomatized heterole‐fused norcaradienes gives the products featuring migratory acylmethyls that are competent for helicenation with the neighboring (hetero) arenes via (formal) dehydrative alkenylation. Such balancing reactivity of heterole‐fused norcaradienes will open up the opportunity for the development of controllable reactions of fused norcaradienes. Facile helicenation of two (hetero) arenes linked by an alkynylcyclopropane: Weakly aromatic heterole‐fused norcaradienes from hydroarylation of heterole‐substituted alkynylcyclopropanes reserve a balancing fluxionality that permits a dearomative and controllable [1,5]‐sigmatropic carbon shift. A following ester‐directed ring‐opening aromatization of the dearomatized heterole‐fused norcaradiene gives the acylmethyl‐shifted aromatization products, which are readily helicenated with the neighboring (hetero) arenes.