To a mixture of ethyl 2-[3-[[3-cyano-5-(3-fluorophenyl)phenyl]methylamino]-2,4-difluoro-phenoxy]acetate (see example 24) (200 mg, 0.45 mmol, 1 eq) and K2CO3 (310 mg, 2.3 mmol, 5 eq) in DMSO (10 mL) at 40° C. was added H2O2 (30% aqueous solution, 10 mL) dropwise. The mixture was stirred for 20 min then cooled to room temperature. Water was added, and the reaction neutralised by addition of diluted HCl. The solid precipitate that formed was collected by filtration, washed with water and dried to give the title compound as white solid (90 mg, 46%).
