Pyridazine derivatives. Part 39: Reactivity of 5-iodopyridazin-3(2H)-ones in palladium-catalysed reactions

In the search for novel antiplatelet agents, convenient and efficient methods for the preparation of 2,5-disubstituted pyridazin-3(2H)-ones are reported that utilise palladium-catalysed cross-coupling reactions. A post-coupling base-promoted isomerisation has been observed during Sonogashira alkynylation of 5-iodopyridazin-3(2H)-ones () with 1-phenyl-2-propyn-1-ol. Variable amounts of phthalazinones were isolated as by-products during the Heck alkenylation of . The usefulness of the hydroxymethyl fragment as a protecting group during the synthesis of 5-substituted pyridazin-3(2H)-ones has been validated.