[O:1]=[C:2]1[S:6][C:5]2[CH:7]=[CH:8][CH:9]=[CH:10][C:4]=2[CH2:3]1.[H-].[Na+].[S:13]1[CH:17]=[CH:16][CH:15]=[C:14]1[NH:18][C:19](=O)[O:20]C1C=CC=CC=1.Cl>CN(C)P(=O)(N(C)C)N(C)C>[S:13]1[CH:17]=[CH:16][CH:15]=[C:14]1[NH:18][C:19]([CH:3]1[C:2](=[O:1])[S:6][C:5]2[CH:7]=[CH:8][CH:9]=[CH:10][C:4]1=2)=[O:20]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.
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