Hydrochloric Acid → 2-Oxo-N-(thiophen-2-yl)-2,3-dihydro-1-benzothiophene-3-carboxamide

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Reaction Steps

A solution of 7.5 g of 2,3-dihydro-2-oxo-benzo[b]thiophen in 50 ml of hexamethylphosphoric acid triamide is added dropwise, with cooling, to a suspension of 2.4 g of a 50% sodium hydride/mineral oil dispersion in 100 ml of hexamethylphosphoric acid triamide, the temperature being kept below 15° during the addition. After stirring for half an hour at room temperature, 52 g of phenyl N-(2-thienyl)-carbamate, dissolved in 50 ml of hexamethylphosphoric acid triamide, are added dropwise, with external cooling. The reaction mixture is stirred for a further 16 hours at room temperature and is poured into a mixture of 200 ml of 2 N hydrochloric acid and 1000 ml of ice-water. An oil separates out and this crystallises after about 2 hours. The crystalline product, which contains solvent, is dissolved in 2 N sodium hydroxide solution and the solution is washed four times with ethyl acetate. The organic phase is washed with water, the aqueous phases are combined and acidified to a pH of 1 and the crude product is filtered off with suction and recrystallised from tetrahydrofuran/ether. N-(2-Thienyl)-2-oxo-2,3-dihydro-3-benzo[b]thiophen-carboxamide with a melting point of 142°-144° (decomposition) is obtained.

Provenance & Evidence