Hydrochloric Acid → 2-Acetyl-5-bromobenzo(b)thiophene

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Reaction Steps

21.0 g of 5-bromo-2-[(N,N-dimethylcarbamoyl)thio]benzaldehyde was dissolved in 50 ml of methyl orthoformate. The resulting solution was mixed with 1.0 g of p-toluenesulfonate, and refluxed under heating for 50 minutes. After cooling, the resulting reaction solution was poured into saturated sodium bicarbonate solution and extracted with benzene. The resulting organic layer was dried to remove the solvent. The residue thus obtained was dissolved in 100 ml of methanol, followed by adding 37 ml of 2N sodium hydroxide and by refluxing under heating for 1 hour in a stream of nitrogen. After cooling, the resulting reaction solution was adjusted to pH 1 with concentrated hydrochloric acid, extracted with benzene, and then dried to remove the solvent. The residue thus obtained was dissolved in 20 ml of acetone and added dropwise, at room temperature, to a stirred mixture consisting of 6.74 g of chloroacetone, 22.1 g of anhydrous potassium carbonate and 150 ml of acetone. After 30 minutes of stirring, the resulting reaction mixture was refluxed under heating for 30 minutes. After cooling, insoluble materials were removed by filtration, and the resulting filtrate was concentrated to dryness. The thus obtained residue was purified by silica gel column chromatography using toluene as an elution solvent and the resulting product was recrystallized from ethanol to obtain 7.5 g of 2-acetyl-5-bromobenzo[b]thiophene.

Provenance & Evidence