Synthesis
General procedure for the synthesis of 5-iodopyridazin-3(2H)-one from 4,5-dichloropyridazin-3(2H)-one: In a sealed tube, 4,5-dichloropyridazin-3(2H)-one (10 g, 60.61 mmol) was mixed with 47% hydriodic acid (75 mL), and the reaction mixture was heated at 150 °C for 25 hours. Upon completion of the reaction, the mixture was filtered and the solid was washed with deionized water (100 mL). Subsequently, the solids were suspended in deionized water (200 mL), heated to 50 °C and sodium thiosulfate was slowly added with stirring until the solution took on a light brown color and precipitate formation was observed. The resulting mixture was filtered and the filtrate was dried under vacuum. The brown solid obtained was washed with ethanol (200 mL) preheated to about 78 °C and filtered again. The red to brown filtrate was dried under vacuum. Finally, the dark brown solid obtained was ground with dichloromethane (20 mL) followed by hexane (4 x 30 mL) and dried under vacuum to give 5-iodo-2H-pyridazin-3-one (8.640 g, 64% yield) as a brown solid. The product could be used in the subsequent reaction without further purification.
References
[1] Patent: US2009/264434, 2009, A1. Location in patent: Page/Page column 29; 47
[2] Bioorganic and Medicinal Chemistry, 2012, vol. 20, # 12, p. 3880 - 3886
[3] Patent: WO2009/142732, 2009, A2. Location in patent: Page/Page column 65-66
[4] Patent: WO2009/152325, 2009, A1. Location in patent: Page/Page column 208-209
[5] Patent: US2008/27041, 2008, A1. Location in patent: Page/Page column 78
