Synthesis, properties, and application of phenanthrenone: an undeveloped building block and a photocatalyst

Abstract

The synthesis, properties, and application of carbonyl-bridged phenanthrene, namely phenanthrenone, are described. A novel synthetic route involving palladium-catalyzed annulation between 4,5-dibromo-9-fluorenone and internal alkynes was developed to streamline the synthesis of phenanthrenone, an underexplored building block. The reaction tolerates a variety of substituents on the alkynes and provides moderate yields. Phenanthrenone derivatives possess the advantages of both fluorenone and phenanthrene backbones, such as extended conjugation, good planarity and rigidity, and tunable energy gaps. These attractive features make phenanthrenone an ideal electron-deficient π-building block for developing novel polycyclic aromatic hydrocarbons. In addition, phenanthrenone derivatives can serve as organic photoredox catalysts for organocatalytic atom transfer radical polymerization and oxidation of alcohol.