A solution of triphenylphosphine (550 mg, 2.1 mmol) in methylene chloride (25 mL) was cooled to 0° C. and then treated with N-bromosuccinimide (374 mg, 2.1 mmol). The reaction mixture was stirred at 0° C. for 30 min and then treated with a solution of (E)-4-cyclopentyl-2-[4-(methanesulfonyl)-3-(trifluoromethyl)-phenyl)-but-2-enoic acid (395 mg, 1.05 mmol) in methylene chloride (5 mL). The clear solution was stirred for 15 min at 0° C. and then allowed to warm to 25° C. where it was stirred for 1.5 h. The reaction mixture was then treated with 2-aminothiazole (320 mg, 3.2 mmol), and the resulting suspension was stirred at 25° C. over the weekend. The reaction mixture was concentrated in vacuo to remove methylene chloride, and the residue was diluted with ethyl acetate (50 mL) and a 1N aqueous hydrochloric acid solution (50 mL). The two layers were separated, and the aqueous layer was extracted with ethyl acetate (1×30 mL). The combined organic extracts were successively washed with a saturated aqueous sodium bicarbonate solution (2×50 mL) and a saturated aqueous sodium chloride solution (1×100 mL). The organic layer was then dried over anhydrous magnesium sulfate, filtered, and concentrated in vacuo. Biotage chromatography (FLASH 40M, Silica, 1/1 hexanes/ethyl acetate) afforded the (E)-4-cyclopentyl-2-(4-methanesulfonyl-3-trifluoromethyl-phenyl)-but-2-enoic acid thiazol-2-ylamide (77 mg, 16%) as an amorphous solid: EI-HRMS m/e calcd for C20H21F3N2O3S2 (M+) 458.0946, found 458.0946.
