Triethylamine → 5-Nitro-3-benzothiophencarboxylic acid amide

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Reaction Steps

5-Nitro-3-benzothiophencarboxylic acid 1b (20 g) was converted into the corresponding carboxylic acid chloride as in Example 2. The acid chloride was dissolved in THF (200 ml) and added dropwise to a solution of 5-chloro-3-(4-piperidinyl)-1H-indole, 9a (19 g) and triethylamine (10 ml) in THF (200 ml) at 0-5° C. The mixture was stirred overnight at room temperature. THF was evaporated. Water was added to the remaining oil. Extraction with dichloromethane (2×100 ml) and work-up of the organic extracts afforded the crude 5-nitro-3-benzothiophencarboxylic acid amide, which was subsequently purified by column chromatography on silica gel (eluted with ethyl acetatelheptane 1:1). Yield 6.6 g, mp: 243-250° C. All of the amide was dissolved in 90% ethanol at reflux. Fe-powder (5 g) and concentrated aqueous HCl were added successively in small portions during 10 minutes. The mixture was refluxed for another 2.5 hours. Inorganic salts were filtered off and ethanol evaporated in vacuo. Water was added to the remaining oil and pH was adjusted to >9 by addition of diluted aqueous NH4OH. Extraction with dichloromethane (2×100 ml) and subsequent work-up of the organic phase yielded 4 g of the 5-amino-3-benzothiophencarboxylic acid amide as an oil. All of this oil was dissolved in methanol (100 ml). 0.5 g of Mg turnings were added. By heating to 35° C. an exothermic reaction started. Mg turnings were added in small portions (3×0.5 g) while keeping the temperature below 45° C. The mixture was finally poured into an aqueous NH4Cl solution and concentrated aqueous HCl (1 ml) was added. Extraction with dichloromethane (2×50 ml) and work-up of the organic extracts as above afforded 2 g of the 5-amino-2,3-dihydrobenzothiophen-3-carboxylic acid amide as an oil. To a suspension of LiAIH4 (0.6 g) in dry THF (50 ml) was added dropwise a solution of all of the carboxamide in THF (50 ml). The mixture was gently refluxed for 2 hours. After cooling to 10° C. water (2.4 ml ) and a 15% aqueous NaOH solution were cautiously added to destroy excess LiAIH4. Inorganic salts were filtered off and washed extensively with THF. The combined THF solutions were evaporated leaving 1.9 g of 3-[1-(5-amino-213-dihydrobenzothiophen-3-ylmethyl)piperidin-4-yl)-5-chloro-1H-indole as an oil.

Provenance & Evidence