To a suspension of N′-hydroxy-3-iodo-1-tosyl-1H-indole-5-carboximidamide (950 mg, 2.09 mmol) in dry THF (10 mL) was added Et3N (1.4 mL, 10.10 mmol) and O-benzotriazole-N,N,N′,N′-tetramethyl-uronium-hexafluoro-phosphate (HBTU) (1.6 g, 4.18 mmol) at 0° C. Trichloroacetyl chloride (0.48 mL, 2.51 mmol) was added portion wise at 0° C. and the reaction was stirred for 16 h at RT. The mixture was treated with H2O (10 mL) and extracted with EtOAc (2×25 mL). The combined organic layers were dried over anhydrous Na2SO4, filtered and concentrated in vacuo. The residue was further with basic alumina chromatography (eluent: 5% EtOAc in petroleum ether) to afford 3-(3-iodo-1-tosyl-1H-indol-5-yl)-5-(trichloromethyl)-1,2,4-oxadiazole (250 mg, 20.8%) as an off white solid. 1H NMR (400 MHz, DMSO-d6): δ 8.26 (s, 1H), 8.21 (d, J=8.8 z, 1H), 8.10 (t, J=1.2 Hz, 1H), 7.99-7.95 (m, 3H), 7.44 (d, J=8.4 Hz, 1H), 2.32 (s, 3H).
