[S:1]1[C:5]2[O:6][C:7]3[CH:15]=[CH:14][CH:13]=[CH:12][C:8]=3[NH:9][C:10](=[O:11])[C:4]=2[CH:3]=[CH:2]1.Cl[CH:17]([O:19]C)Cl.[Cl-].[Al+3].[Cl-].[Cl-]>C(Cl)Cl>[CH:17]([C:2]1[S:1][C:5]2[O:6][C:7]3[CH:15]=[CH:14][CH:13]=[CH:12][C:8]=3[NH:9][C:10](=[O:11])[C:4]=2[CH:3]=1)=[O:19]Thieno[2,3-b][1,5]benzoxazepin-4(5H)-one (1.9 g) was suspended in methylene chloride (20 ml) and dichloromethylmethyl ether (4.0 g) was added. To this reaction system was added aluminum chloride (4.6 g) under ice-cooling and the mixture was stirred for 15 minutes. The reaction mixture was poured into ice water-chloroform and the mixture was stirred at room temperature for 20 minutes. The aqueous layer was extracted 5 times with chloroform and the combined organic layer was dried over sodium sulfate. The solvent was evaporated under reduced pressure and diisopropyl ether was added to the residue. The precipitated crystals were collected by filtration to give 2-formylthieno[2,3-b][1,5]benzoxazepin-4(5H)-one (1.2 g).
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