Lewis Acid‐Catalyzed Unusual (4+3) Annulation of para‐Quinone Methides with Bicyclobutanes: Access to Oxabicyclo[4.1.1] octanes

Over the past few years, there has been a surge of interest in the chemistry of bicyclobutanes (BCBs). Although BCBs have been used to synthesize bicyclo[2.1.1]hexanes and bicyclo[3.1.1]heptanes, the synthesis of bicyclo[4.1.1]octanes has remained elusive. Herein, we report the first Lewis acid-catalyzed unexpected (4+3) annulation of para-quinonemethides (p-QMs) with BCBs allowing the synthesis of oxabicyclo[4.1.1]octanes proceeding under mild conditions. With 5 mol % of Bi(OTf)