Bromine → 3-bromo-5-methyl-4,5-dihydro-6H-cyclopenta[b]thiophen-6-one

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Reaction Steps

A total of 129 g (0.85 mol) of 5-methyl-4,5-dihydro-6H-cyclopenta[b]thiophen-6-one in 130 ml of CHCl3 were added to a suspension of 250 g (1.89 mol) of AlCl3 (anhydrous powder) in 350 ml of CHCl3 at 0° C. over 0.5 h. The reaction mixture was stirred for 10 min at this temperature; then a solution of 46.7 ml of Br2 (0.91 mol) in 90 ml of CHCl3 was added dropwise for 1 h. The resulting mixture was stirred for 1 h at room temperature and, then, poured over 2000 cm3 of ice. The organic layer was separated. The aqueous layer was extracted with 4×200 ml of CH2Cl2. The combined organic fractions were washed with 1000 ml of the saturated aqueous Na2CO3, dried over K2CO3, passed through a short Silica Gel 60 column (40-63 μm, d 40 mm, l 50 mm), and evaporated to dryness. Fractional distillation gave white crystalline product, b.p. 128° C./0.8 mm Hg. Yield 185 g (94%).

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