[Cl-].[CH3:2][O:3]C[P+](C1C=CC=CC=1)(C1C=CC=CC=1)C1C=CC=CC=1.C([Li])CCC.[S:29]1[C:35]2[CH:36]=[CH:37][CH:38]=[CH:39][C:34]=2[C:33](=O)[CH2:32][CH2:31][CH2:30]1.Cl(O)(=O)(=O)=O>O1CCCC1.CCCCCC>[S:29]1[C:35]2[CH:36]=[CH:37][CH:38]=[CH:39][C:34]=2[CH:33]([CH:2]=[O:3])[CH2:32][CH2:31][CH2:30]1A solution of 20.0 g of methoxymethyltriphenylphosphonium chloride in 60 ml of absolute tetrahydrofuran was treated dropwise at 0° C. under argon with 43 ml of 1.4N n-butyllithium in hexane. The mixture was stirred for 1/4 hour. Thereafter, the mixture was treated with 8.02 g of 3,4-dihydro-1-benzothiepin-5(2H)-one in a small amount of tetrahydrofuran. After 5 minutes, the cooling bath was removed and the reaction mixture was stirred at room temperature for an additional 11/2 hours. Thereafter, the reaction mixture was partitioned between petroleum ether and ethanol/water (8:2). The lighter phase was washed with water, dried over sodium sulfate and evaporated. There were obtained 11.8 g of crude product which were dissolved in 80 ml of tetrahydrofuran and treated under argon with 100 ml of 35% perchloric acid. The reaction mixture was stirred overnight, poured on to ice, extracted with ether, washed with 5% sodium carbonate solution, dried and evaporated. Chromatography on silica gel (petroleum ether/ethyl acetate 92:8) yielded 5.04 g of 2,3,4,5-tetrahydro-1-benzothiepine-5-carboxaldehyde as a colorless oil.
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