[N:1]1([C:7]2[C:8]3[CH:21]=[CH:20][CH:19]=[CH:18][C:9]=3[S:10][C:11]=2[C:12]2[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=2)[CH2:6][CH2:5][NH:4][CH2:3][CH2:2]1.C=O.[CH:24](O)=O.N>CO.O>[CH3:24][N:4]1[CH2:3][CH2:2][N:1]([C:7]2[C:8]3[CH:21]=[CH:20][CH:19]=[CH:18][C:9]=3[S:10][C:11]=2[C:12]2[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=2)[CH2:6][CH2:5]1
A mixture of 7.0 g (24 mmole) of 3-(piperazino)-2-phenyl-benzo(b)thiophene, 3.5 milliliters of formalin at 35% (41 mmole) and 3.5 milliliters of formic acid at 98-100% (92 mmole) is refluxed for 1 hour. After cooling, it is poured into water, made alkaline with ammonia and extracted with CH2Cl2. By evaporating the organic phase dried over K2CO3, 7.2 g (98% of theory) of 3-(4'-methylpiperazino)-2-phenyl-benzo(b)thiophene are obtained: beige crystals, mp 118°-120° (methanol).
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