1-Ethyl-3-(3'-dimethylaminopropyl)carbodiimide → ethyl 1-{2-[2-(tert-butoxycarbonyl)hydrazino]-2-oxoethyl}-1H-pyrazole-4-carboxylate

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Reaction Steps

A solution of the compound (9.4 g) obtained in Example 115b, N-[3-(dimethylamino)propyl]-N′-ethylcarbodiimide (18.1 g) and 1-hydroxybenzotriazole (6.5 g) in dichloromethane (100 mL) was cooled to −20° C., and a solution of tert-butyl hydrazinecarboxylate (9.5 g) in dichloromethane (20 mL) was added dropwise. The reaction mixture was stirred at room temperature overnight, poured into water, and the mixture was extracted with ethyl acetate. The ethyl acetate layer was washed with saturated brine, dried over sodium sulfate, and concentrated under reduced pressure. The residue was purified by column chromatography (carrier: silica gel, eluent: petroleum ether/ethyl acetate/triethylamine=10/1/0.001) to give ethyl 1-{2-[2-(tert-butoxycarbonyl)hydrazino]-2-oxoethyl}-1H-pyrazole-4-carboxylate (9.2 g) as a colorless solid. The solid was dissolved in ethyl acetate (50 mL), and hydrogen chloride-ethyl acetate (50 mL) was added. The mixture was stirred at room temperature for 1 hr, and the precipitate was collected by filtration to give the title compound (6.0 g) as a colorless solid.

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