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A mixture of 4-nitrobenzamide oxime (4 g) and ethyl chlorooxoacetate (3.01 g) in dioxane (200 ml) was refluxed for 1 hour, and then borontrifluoride (1 ml) was added thereto. The whole mixture was refluxed for 12 hours. After being cooled to room temperature, the solvent was evaporated in vacuo. The residue was diluted with ethyl acetate (100 ml), washed with a saturated potassium carbonate aqueous solution, dried over magnesium sulfate and evaporated in vacuo. The residue was purified by column chromatography on silica gel with a mixture of dichloromethane and hexane (1:1) as eluent. The fractions containing the object product were collected and evaporated in vacuo to afford 5-ethoxycarbonyl-3-(4-nitrophenyl)-1,2,4-oxadiazole.

1. temperaturewas refluxed for 1 hour
2. temperatureThe whole mixture was refluxed for 12 hours
3. customthe solvent was evaporated in vacuo
4. additionThe residue was diluted with ethyl acetate (100 ml)
5. washwashed with a saturated potassium carbonate aqueous solution
6. dry with materialdried over magnesium sulfate
7. customevaporated in vacuo
8. customThe residue was purified by column chromatography on silica gel with a mixture of dichloromethane and hexane (1:1) as eluent
9. additionThe fractions containing the object product
10. customwere collected
11. customevaporated in vacuo