Oxidative Annulation of Aldehydes, 5‐Aminopyrazoles, and Nitriles: Synthesis and Applications of Pyrazolo[3,4‐d]Pyrimidines

Abstract The oxidative [3+2+1] annulation reaction of aldehydes, 5‐aminopyrazoles, and nitriles is achieved under the oxidation of I 2 /O 2 , affording various valuable pyrazolo[3,4‐ d ]pyrimidines in 27%–91% yields. The salient feature of this reaction is transition‐metal free, operationally simple, broad substrate scope, good functional group tolerance, and gram‐scalable. Remarkably, the corresponding products exhibited intriguing photophysical properties such as Aggregation‐Induced Emission (AIE) and intramolecular charge transfer (ICT) and showed good potential to specifically light up lipid droplets (LDs) in living cells with bright fluorescence, low cytotoxicity, and good photostability. magnified image