π-Stacking-Controlled Dearomatic Sulfur-Shifted Ene Reaction of Ketenes and Polycyclic Arylthiiranes: Access to Areno[]-ε-thiolactones.

Electrophilic ring-expansion of polycyclic arylthiiranes and ketenes generated from alkoxy/aryloxyacetyl chlorides in the presence of triethylamine (TEA) is developed and provides a new strategy for the synthesis of areno[]-ε-thiolactones, areno[]thiepinones, directly without catalysts or additives. This strategy features atom- and step-economic one-pot characteristic via a tandem sequence of in situ ketene generation, π-stacking-controlled dearomatic sulfur-shifted ene, and aromatization. The current reaction is a novel strategy of electrophilic ring expansions of three-membered saturated heterocycles.