To a solution of 1,1-dimethylethyl(3-chloro-5-fluorophenyl)carbamate (7.34 g, 30 mmol) in tetrahydrofuran (200 mL, Aldrich) at −78° C. was slowly added tBuLi as a 1.7M solution in pentane (46 mL, 78 mmol, 2.6 equiv.). The resulting bright yellow solution was maintained at −78° C. for 3 hours, at which time methylchloroformate (3.02 mL, 39 mmol, Fluka) was added dropwise. After 45 minutes aqueous ammonium chloride (100 mL) was added and the reaction was warmed to room temperature. The organic layer was washed with brine, taken to a residue under reduced pressure, and purified by chromatography on SiO2 (10 to 30% ethyl acetate/hexanes) to afford methyl 4-chloro-2-({[(1,1-dimethylethyl)oxy]carbonyl}amino)-6-fluorobenzoate as a pale yellow oil (6.4, 70% yield) as a roughly 5:1 mixture with 1,1-dimethylethyl[5-chloro-2-(2,2-dimethylpropanoyl)-3-fluorophenyl]carbamate which was removed in the subsequent step. 1H NMR (400 MHz, CDCl3) δ ppm 1.52 (s, 9 H), 3.95 (s, 3 H), 6.76 (d, J=2.20 Hz, 1 H), 6.78 (d, J=4 Hz, 1H) 8.31-8.34 (m, 1 H).
