Synthesis of Pyrimido[1,2- a ]indolediones and Pyrimidinediones via [4+2] Annulation of 2 H -Azirine-2-carbaldehydes.

NHC-catalyzed [4+2] annulation of 2 H -azirine-2-carbaldehydes with ketimines and isocyanates has been developed, providing straightforward synthetic protocols for constructing structurally intriguing pyrimido[1,2- a ]indolediones and pyrimidinediones under mild conditions with excellent yields. This protocol can be used to synthesize the core skeleton of pharmaceutically important drugs and pyrimido[1,2- a ]indoledione-containing natural products, making it potentially valuable for creating biologically active derivatives.