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

Abstract

AbstractOver 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)3, the reaction afforded the (4+3) annulated product in high regioselectivity and good functional group compatibility via a simultaneous Lewis acid activation of BCBs and p‐QMs. The reaction is likely initiated by the 1,6‐addition of Lewis acid activated BCBs to p‐QMs followed by the C2‐selective intramolecular addition of the phenol moiety to the generated cyclobutyl cation intermediate. Moreover, detailed mechanistic studies provided insight into the mechanism of the reaction.