Chloroform hexane → Ethyl 2-amino-4-chloro-1H-indole-3-carboxylate

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Reaction Conditions

Reaction Steps

4 (18 g, 67 mmol), in 250 mL glacial acetic acid, was treated with a single charge of 18 g of zinc dust. The mixture was heated at 55° C. for 45 minutes. Later, 6 g more zinc dust was added. After heating for another 105 minutes, the yellow mixture was filtered through a pad of celite. The pad was washed with acetic acid and the filtrate was concentrated to a residue that was distributed between chloroform and water. The organic phase was washed with NaHCO3 (5%) to provide a pink precipitate which was filtered, dried over P2O5, dissolved in methanol, added silica gel and converted to a silica gel plug by removing the solvent under reduced pressure. The plug was transferred on top of a column packed with silica gel, ten times the weight of plug, eluted with hexane, chloroform, 5% ethylacetate in chloroform and 10% ethylacetate in chloroform. Fractions containing the product 5 (TLC) were pooled and evaporated to give a pink solid. The overall yield from 3 to 5 was 63%. TLC Rf 0.187 (hexane-chloroform 1:1); mp 140-142° C.; 1H NMR (DMSO-d6) δ 1.25-1.28 (t, 3H, CH3); 4.18-4.20 (q, 2H, CH2); 6.85 (bs, 2H, 2-NH2, exch); 6.92-7.09 (m, 3H, phenyl); 10.93 (bs, 1H, 9-NH, exch). Anal. Calculated (C11H11ClN2O2): C, 55.36; H, 4.65; N, 11.74; Cl, 14.85. Found: C, 55.39; H, 4.60; N, 11.65; Cl, 14.96.

Provenance & Evidence