Brønsted acid-catalyzed synthesis of spirocyclobutanes via heteroannulation of vinyloxyphenylbicyclobutanes with water.

We report a perchloric acid-catalyzed heteroannulation for the synthesis of spirocyclobutanes using vinyloxyphenylbicyclobutanes with water. This metal-free reaction yields high product outputs and is consistent with the formation of a cyclobutene intermediate originating from an isomerization of a bicyclobutane.