Potassium Carbonate → [3,5-dimethyl-1-(2-chloro-4-nitrobenzyl)-1H-pyrazol-4-yl]acetic acid tert-butyl ester

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To a solution of (3,5-dimethyl-1H-pyrazol-4-yl)-acetic acid tert-butyl ester (2.6 g, 12.4 mmol, preparation according to WO2007/141267 by using 2,4-pentanedione instead of 3,5-heptanedione) and 2-chloro-4-nitrobenzyl bromide (3.11 g, 12.4 mmol) in acetonitrile (30 mL) is added K2CO3 (2.575 g, 18.6 mmol) and the mixture is stirred for 48 hours at room temperature and after that 2 hours at 60° C. The solid is filtered off and the solvent is removed by evaporation. The residue is dissolved in dichloromethane/water. After extraction with dichloromethane the organic layer is dried over MgSO4 and evaporated under reduced pressure to yield 4.4 g of [3,5-dimethyl-1-(2-chloro-4-nitrobenzyl)-1H-pyrazol-4-yl]acetic acid tert-butyl ester (ESI mass spectrum: [M+H]+=380). b) To a solution of [3,5-dimethyl-1-(2-chloro-4-nitrobenzyl)-1H-pyrazol-4-yl]acetic acid tert-butyl ester (4.40 g, 11.6 mmol) in methanol (80 mL) is added Raney nickel (440 mg) and the mixture is hydrogenated at 50 psi and room temperature for 12 hours. The catalyst is filtered off and the filtrate is concentrated under reduced pressure to yield 2.4 g of the title compound (ESI mass spectrum: [M+H]+=350; Retention time HPLC: 0.76 min (method D)).

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