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Dibromoformaldoxime (407 mg, 2.07 mmol) (prepared via the procedure of J C Rohloff, et. al., Tetrahedron Lett 1992, 33:3113-6), and ethyl propiolate (311 mg, 3.17 mmol) were dissolved in 10 ml of 50% aqueous EtOH. While stirring, a solution of 243 mg (2.43 mmol) of potassium bicarbonate in 5 ml of water was added dropwise over 1 h. The resulting solution was stirred for an additional 4 h, diluted with 25 ml of water, and extracted with chloroform (3×25 ml). The combined organic extract was dried over sodium sulfate and concentrated in vacuo to a colourless oil, 345 mg (78% yield) as a 7:1 mixture of the 5- and 4-carboxylates.

1. stirringThe resulting solution was stirred for an additional 4 h
2. extractionextracted with chloroform (3×25 ml)
3. extractionThe combined organic extract
4. dry with materialwas dried over sodium sulfate
5. concentrationconcentrated in vacuo to a colourless oil, 345 mg (78% yield) as a 7:1 mixture of the 5- and 4-carboxylates