Functionalized Heteroarylpyridazines and Pyridazin-3(2<i>H</i>)-one Derivatives via Palladium-Catalyzed Cross-Coupling Methodology

A general method for the synthesis of functionalized pyridazinylboronic acids/esters is described involving a directed ortho metalation (DoM)boronation protocol (Schemes and ). A comprehensive study of the reactivity of the C−B bond in palladium-catalyzed cross-couplings with aryl/heteroaryl halides is presented. Aryl-/heteroarylpyridazines are thereby obtained in synthetically viable yields (typically 40−75%) although in some cases competing protodeboronation has been observed. A series of pyridazin-3(2H)-one derivatives, including 4,6-diaryl/heteroaryl derivatives, have been obtained from the corresponding 3-methoxypyridazines in straightforward procedures (Schemes and ). Several X-ray crystal structures of aryl-/heteroarylpyridazines and derived pyridazin-3(2H)-one derivatives are reported. These multi-ring systems are of considerable interest in contemporary N-heterocyclic chemistry.