Triethylamine → (7-Fluoro-1,2,3,4-tetrahydro-2,3-dioxoquinoxalin-1-yl)-methanephosphonic acid diethyl ester

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Reaction Steps

660 mg of N(-2-amino-5-fluorophenyl)-aminomethanephosphonic acid diethyl ester is introduced in 70 ml of absolute tetrahydrofuran with 509 mg of triethylamine. A solution of 685 mg of oxalic acid ethyl ester chloride in 30 ml of tetrahydrofuran is slowly instilled into this solution. The batch is stirred for 4 hours at room temperature. After suctioning-off of the precipitated salts, the filtrate is concentrated by evaporation, boiled in a mixture of 23 ml of ethanol and 23 ml of 1N hydrochloric acid for 2 hours at 110° C. bath temperature. It is evaporated to dryness and the residue is chromatographed on silica gel with methylene chloride:ethanol=10:1. 561 mg of (7-fluoro-1,2,3,4-tetrahydro-2,3-dioxoquinoxalin-1-yl)-methanephosphonic acid diethyl ester is obtained.

Provenance & Evidence