Triphenylphosphine → Dimethyl 4-nitro-1-(2-propoxyethyl)-1H-pyrazole-3,5-dicarboxylate

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Diisopropyl azodicarboxylate (14.2 mL, 70 mmol) was added to an ice-cooled solution of 4-nitro-1H-pyrazole-3,5-dicarboxylic acid dimethyl ester (EP 1241170, prep 10) (15 g, 60 mmol), 2-propoxyethanol (8.2 mL, 70 mmol) and triphenylphosphine (18.9 g, 70 mmol) in tetrahydrofuran (150 mL), and the reaction stirred at 0° C. for 2.5 hours, then allowed to stir at room temperature for a further 18 hours. The reaction was concentrated in vacuo and the residue purified by column chromatography on silica gel using ethyl acetate:pentane as eluant, and then re-columned using dichloromethane as eluant to afford the title compound as a solid, 14 g.

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