[C:1]([C:4]1[S:5][C:6]2[C:13]([Br:14])=[CH:12][CH:11]=[CH:10][C:7]=2[C:8]=1[CH3:9])(=O)[CH3:2].C(O)COCCO.O.NN.[OH-].[K+]>O>[CH2:1]([C:4]1[S:5][C:6]2[C:13]([Br:14])=[CH:12][CH:11]=[CH:10][C:7]=2[C:8]=1[CH3:9])[CH3:2]8.6 g (32 mmol) of 2-acetyl-3-methyl-7-bromobenzothiophene and 175 ml of diethylene glycol are placed in a 500 ml three-necked flask equipped with a distillation system. The mixture is stirred at 30° C. for 5 minutes and 4.2 ml (56 mmol) of hydrazine monohydrate are added dropwise. The mixture is heated at 40° C. for 5 minutes and 4.3 g (76.6 mmol) of powdered potassium hydroxide are added. The temperature is brought to 110° C. for 40 minutes and then to a 160° C. for 100 minutes, in order to allow the water present in the reaction mixture to be distilled off. The mixture, once cooled, is then poured onto crushed ice and extraction is carried out with ethyl acetate (3×200 ml). The organic phases are combined, washed with 200 ml of a saturated sodium bicarbonate solution and 2×200 ml of water, dried over magnesium sulphate and concentrated. The residue is purified by chromatography on a silica column (elution solvent: cyclohexane). 7.62 g (Yield: 84%) of 2-ethyl-3-methyl-7-bromobenzothiophene are obtained in the form of a yellow oil.
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