Chlorosuccinimide → tert-butyl 5'-(5-(3,5-dichloro-4-fluorophenyl)-5-(trifluoromethyl)-1,4,2-dioxazol-3-yl)-3'H-spiro[azetidine-3,1'-isobenzofuran]-1-carboxylate

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To a stirred solution of tert-butyl 5′-((hydroxyimino)methyl)-3′H-spiro[azetidine-3,1′-isobenzofuran]-1-carboxylate (Preparation 43) (0.5 g, 1.645 mmol, 1 eq) in DMF (6.5 mL) was added NCS (0.218 g, 1.645 mmol, 1 eq). Reaction mixture was stirred at 55° C. for 1 hour under nitrogen atmosphere. After 1 hour (chloro intermediate formation), 1-(3,5-dichloro-4-fluoro-phenyl)-2,2,2-trifluoro-ethanone (0.437 g, 1.678 mmol, 1.02 eq) was added followed by addition of sodium bicarbonate (0.140 g, 1.678 mmol, 1.02 eq) at room temperature. Resulting reaction mixture was stirred at 55° C. for 3 hours under nitrogen atmosphere. After complete consumption of starting material, reaction mixture was quenched by water (10 mL) and extracted with ethyl acetate (3×50 mL). Combined organic phase was washed with brine solution (20 mL), dried over anhydrous Na2SO4 and concentrated under reduced pressure to get brown thick oil (0.6 g, crude). Crude compound was purified by Combiflash using 40 g Redisep column. Desired compound was eluted in 25% ethyl acetate in hexane to afford title compound as colorless thick oil (0.33 g, impure). 1H NMR (400 MHz, CDCl3) δ: 1.46 (s, 9H), 4.11 (d, J=10.04 Hz, 2H), 4.32 (d, J=9.92 Hz, 2H), 5.15 (s, 2H), 7.56-7.58 (m, 1H), 7.64-7.68 (m, 3H), 7.86 (d, J=8.04 Hz, 1H), 8.02-8.04 (dd, J1=6.12 Hz, J2=0.64 Hz, 1H). LC-MS (m/z): No ionization.

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