Imidazolium-dithiocarboxylate zwitterion-catalyzed synthesis of fully substituted spiro-glutarimides via [3 + 3] annulation of cyclopropenones

Abstract

An organocatalytic [3 + 3] annulation reaction of cyclopropenones and cyclic β-ketoamides has been reported for the synthesis of fully substituted spiro-glutarimides. Under the catalysis of imidazolium-dithiocarboxylate zwitterions (NHC·CS₂), cyclopropenones react with cyclic ketoamides through a tandem ring opening/intermolecular nucleophilic substitution/intramolecular nucleophilic addition/tautomerization process to afford a diverse range of spirocyclic glutarimide derivatives containing one all-carbon quaternary spirocenter in high yields with excellent diastereoselectivity. The reaction can be scaled up easily and the stable NHC·CS₂ zwitterion catalyst can be recovered and reused at least four times.