3‐(Methoxycarbonyl)Cyclobutenone as a Reactive Dienophile in Enantioselective Diels–Alder Reactions Catalyzed by Chiral Oxazaborolidinium Ions

Cyclobutenone has been used as a highly reactive dienophile in Diels–Alder reactions, however, no enantioselective example has been reported. We disclose herein a chiral oxazaborolidine‐aluminum bromide catalyzed enantioselective Diels–Alder reaction of 3‐alkoxycarbonyl cyclobutenone with a variety of dienes. Furthermore, a total synthesis of (−)‐kingianin F was completed for the first time via enantioenriched cycloadduct bicyclo[4.2.0]octane derivative.