Innovative advancements in transition metal-catalyzed C(sp2)-H bond activation of phthalazinone: Unlocking the gateway to diverse hybrid polyheterocyclic architectures

Phthalazinones, a fused diaza heterocycles have been recognized as remarkable structural leads in medicinal chemistry owing to its wider application in pharmaceutical and agrochemical industries. Moreover, having unique structural feature and potent biological activities, this scaffold allures the attention of synthetic chemists toward selective activation and functionalization of CH bonds to synthesize its fused polycyclic frameworks. To attain this goal, transition-metal-catalyzed directing group-assisted inert Csp²-H functionalization has pooled up powerful strategies into modern chemistry toolbox in the last decade. The regioselective activation and annulation of CH bonds are improving the synthetic approach and revolutionizing conventional cross-coupling techniques in current research. In this domain, the selective functionalization of CH bonds in heteroarenes is primarily accomplished by Ru, Rh, Ir, and Pd metal complexes and their salts. This review primarily focuses on recent developments in the selective activation and functionalization of CH bonds and the annulation of phthalazinones to synthesize their fused polycyclic frameworks. It explores their interactions with metal catalysts, along with various coupling partners such as amides, imides, ynones, vinylene carbonates, propargyl alcohols, alkenes, and alkynes which in turn led to the formation of different types of CC and CN bonds through selective CH bond activation and subsequent annulation leading to pi-extended heterocycles.