Synthesis of diverse 4,5-dihydro-3(2H)-pyridazinones on Wang resin

An efficient solid-phase synthesis of structurally diverse 4,5-dihydro-3(2H)-pyridazinones is described using readily available substituted 4-oxo-butanoic acids. Polymer-supported gamma -ketoesters prepared from Wang resin reacted with several hydrazines to afford the corresponding hydrazones. A protocol developed in mild conditions without isolating the intermediate hydrazone led to pyridazinones in good yields after a cyclization cleavage approach. This successful strategy represents an attractive method for a rapid synthesis of heterocyclic libraries for biological evaluation.