A mixture of L-carvone 4-methyl-thiosemicarbazone 2 (16.8 g, 70.8 mmol) and sodium ethoxide (4.87 g, 71.6 mmol) in anhydrous ethanol (150 mL) was stirred at room temperature, and then ethyl bromoacetate (11.9 g, 71.3 mmol) was poured into the solution under continuous stirring. The reaction mixture was heated to reflux and kept for 4 h. After that, the reaction mixture was cooled down to room temperature, and the resulting precipitate was filtered out to obtain L-carvone-based intermediate 3 as a white solid with a yield of 93.0%.
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