Tert-Butylamine → 5-ethyl-N-tert. butyl-furan-2-sulfonamide

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Analogous to the preparation of the 5-methyl-2-sulfamoyl-furan-3-carboxylic acid (see starting compound of Example 1), 2-ethyl furan was sulfonated with sulfur trioxide-pyridine-complex into the sodium salt of the 5-ethyl-furan-2-sulfonic acid with a yield of 32.5% of theory. After chlorinating it with phosphorus pentachloride and reacting it with tert. butyl amine, 5-ethyl-N-tert. butyl-furan-2-sulfonamide [(m.p. 71°-72° C. from petroleum ether); 1H-NMR (CDCl3): δ=6.95 (d, 1, J=2 Hz, 3-H), 6.15 (d, 1, J=2 Hz, 4-H), 4,7 (s, 1, NH, exchangeable), 2.73 (q, 2, CH2), 1.30 (m, 12, --CH2 --CH3 and C(CH3)3)] was obtained with a yield of 48% of theory. The two subsequent reactions were also performed in analogy to the preparation of the 5-methyl-furan compound: By metalizing with butyl lithium and by carboxylating with carbon dioxide, the 5-ethyl-2-(N-tert. butyl)-sulfamoyl-furan-3-carboxylic acid (m.p. 118°-119° C. from cyclo hexane) was obtained with a yield of 59% of theory, which was heated under dry conditions at 160° C. for 2 hours. 5-Ethyl-2-sulfamoyl-furan-3-carboxylic acid [m.p.: 186° C. (from ethyl acetate), 1 H-NMR ([d6 ]=DMSO); δ=6.6 (s, 1, 4-H), 2.73 (q, 2, CH2), 1.25 (t, 3, CH3) and two exchangeable protons] was obtained with a yield of 87% of theory.

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