Knoevenagel condensation of 4,5- and 1,8-diazafluorenes

Diazafluorenylidenes are potential antitumor agents, ligands, and functional materials. However, there are currently only limited methods for their synthesis, which are complicated and typically based on modifications of 4,5-diazafluorenone. Herein, we systematically studied the Knoevenagel condensation of both 4,5- and 1,8-diazafluorenes with aromatic aldehydes and evaluated the diazafluorenes’ nature and solvent influence on the mechanism and reactivity. We also identified conditions allowing the preparation of both 4,5- and 1,8-diazafluorenylidenes in yields up to 85% minimizing complicated synthetic or experimental workup procedures. Additionally, the condensation of diazafluorenes with ketones resulted in unique di(pyridin-2-yl)methylene)-9 H -diazafluorenes being electron-deficient ligands and functional materials.