Hydrochloric Acid → 3,4-diethyl 1H-pyrazole-3,4-dicarboxylate

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Under an atmosphere of argon, hydrazine monohydrate hydrochloride (1.91 g, 28 mmol) and HCl (36.5% in water, 2.8 ml) were added to a solution of 2-dimethylaminomethylene-3-oxo-succinic acid diethyl ester (6.8 g, 28 mmol, obtained by the method of Hanzlowsky et al., J. Heterocyclic Chem. 2003, 40(3), 487-498) in ethanol (100 ml). The mixture was heated to 60° C. (3 h). The solvent was evaporated, and the residue was taken up in dichloromethane and washed (water). The organic layer was dried (Na2SO4), the solvent was evaporated and the title compound (1.81 mg, 31%) was isolated from the mixture by column chromatography (silica gel, heptane:ethyl acetate=100:0-60:40). MS (m/e)=383.3 [M+H+].

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