Dearomatization of benzopyrylium triflates with sulfoxonium ylides.

Benzopyrylium triflates react with sulfoxonium ylides to give rise to cyclopropanated products in up to 90% yield as a single diastereomer. The cyclopropanated products can easily undergo acid-mediated ring-expansion to afford benzo[]oxepines. Control over the absolute stereochemistry of the process is possible when the reaction is executed under the influence of a suitable anion-binding catalyst.