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0 °C

To a suspension of 29.3 g (220 mmol) of AlCl3 in 40 ml of chloroform a solution of 16.4 g (100 mmol) of 4,5-dimethyl-4,5-dihydro-6H-cyclopenta[b]thiophen-6-one in 15 ml of chloroform was added while vigorously stirring for 30 min at 0° C. This mixture was stirred for 15 min; then, a solution of 5.48 ml (17.1 g, 107 mmol) of bromine in 10 ml of chloroform was added dropwise over 1 h at 0° C. The resulting mixture was stirred for 1.5 h at room temperature and then poured on 200 cm3 of ice. The mixture was acidified with 4 M HCl to pH 1. The organic layer was separated, and the aqueous layer was washed with 3×100 ml of dichloromethane. The combined organic fractions were dried over K2CO3 and evaporated to dryness. The product was isolated by vacuum distillation, bp 110-112° C./2 mm Hg. Yield 22.1 g (91%).

1. additionwas added
2. stirringThis mixture was stirred for 15 min
3. stirringThe resulting mixture was stirred for 1.5 h at room temperature
4. customThe organic layer was separated
5. washthe aqueous layer was washed with 3×100 ml of dichloromethane
6. dry with materialThe combined organic fractions were dried over K2CO3
7. customevaporated to dryness
8. customThe product was isolated by vacuum distillation, bp 110-112° C./2 mm Hg