To a solution of (2-amino-4,5-difluoro-phenyl)-carbamic acid tert-butyl ester (2.50 g, 10.24 mmol, 1.0 equiv; example 1, intermediate b) in methanol (30 mL) was added cyclohexanecarbaldehyde (1.15 g, 1.23 mL, 10.24 mmol, 1.0 equiv; [2043-61-0]) and the mixture stirred at rt. After 30 min, 2,6-dimethoxy-nicotinic acid (1.88 g, 10.24 mmol, 1.0 equiv; [CAS RN 16727-43-8]) and isocyanomethyl-benzene (1.20 g, 1.25 mL, 10.24 mmol, 1.0 equiv; [931-53-3]) were added and stirring continued at rt for 2 h. A solution of 4 M HCl in dioxane (20 mL) was added and the reaction mixture stirred at rt overnight. The solution was concentrated by evaporation under reduced pressure, the pH adjusted to 9 by addition of a solution of 1 M NaHCO3 and the aqueous layer extracted with dichloromethane. The combined organic phases were dried over MgSO4 and concentrated by evaporation under reduced pressure. The crude material was purified by silica column chromatography using a MPLC system (CombiFlash Companion, Isco Inc.) eluting with a gradient of heptane/ethyl acetate to give 3.57 g (60%) of the title compound. MS (ES+): 522 (M+H).
