Regorafenib monohydrate synthesis

Among several published synthesis, the most likely process scale synthesis will be highlighted from the two published syntheses, and this is described in the scheme. Commercially available picolinic acid (148) was heated with thionyl chloride to provide the crude intermediate 4-chloro-2- pyridyl acid chloride which was subsequently reacted with aqueous methyl amine in toluene to give 4- chloro-2-methylcarboxamide as its hydrochloride salt 149 in quantitative yield after treatment with acetyl chloride in toluene and ethanol. The hydrochloride salt was free based with sodium hydroxide and then immediately reacted with imine 150 (formed upon exposure to 4-amino-3-fluorophenol (153) in refluxing 3-methyl 2-butanone) in base to provide diaryl ether 151 in 84% yield. Reaction of amine 151 with the commercially available isocyanate 152 ultimately delivered regorafenib hydrate (XXIII) in 83% yield.