Access to Polysubstituted Pyrimidin-2-ones by Pd-Catalyzed [2 + 2 + 2] Cycloaddition of Alkyne-Tethered Malononitriles and Isocyanates

Transition-metal-catalyzed [2 + 2 + 2] cycloaddition reactions of alkynes, nitriles, and other π partners have been recognized as economic strategies to assemble aza-six-membered rings, but access to pyrimidin-2-ones is not disclosed. Herein, we report a palladium-catalyzed [2 + 2 + 2] cycloaddition of 1,3-diyne-substituted malononitriles and isocyanates for the construction of polysubstituted pyrimidin-2-ones. This reaction features a broad substrate scope and moderate to high yields. Conjugated pyrimidin-2-one acting as a fluorophore showcased potential as a fluorescent chemosensor for Fe(III) detection.