Isothiourea-Catalyzed [2+2] Cycloaddition of C(1)-Ammonium Enolates and N-Alkyl Isatins

Enantioselective [2 + 2] cycloaddition of C(1) ammonium enolates generated catalytically using the isothiourea HyperBTM with N-alkyl isatins gives spirocyclic beta-lactones. In situ ring opening with an amine nucleophile generates isolable highly enantioenriched products in up to 92:8 dr and in > 99:1 er.

Automated summary

This study reports a method for enantioselective [2 + 2] cycloaddition of C(1) ammonium enolates generated catalytically using the isothiourea HyperBTM with N-alkyl isatins, which leads to the formation of spirocyclic beta-lactones. In situ ring opening with an amine nucleophile generates isolable highly enantioenriched products with a diastereomeric ratio of up to 92:8 and an enantiomeric ratio of > 99:1.