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Step 2: Preparation of 4-bromo-2-ethylphenylboronic acidTo a solution of <strong>[175278-30-5]4-bromo-2-ethyl-1-iodobenzene</strong> (80 g, 0.25 mol) in tetrahydrofuran (800 ml) at - 75 0C is added n-butyl lithium (1.6 M in hexanes, 188 ml, 0.3 mol) dropwise maintaining the temperature of the reaction mixture below -70 °C. When the addition is complete the mixture is stirred at -75 0C for an additional 30 minutes and then trimethyl borate (153.7 g, 1.48 mol) is added dropwise. After the addition is complete the reaction is stirred at -75 0C for 1 hour, then allowed to come to room temperature and stirred for 2 hours, followed by cooling in an ice bath and acidification with 0.5 N aqueous hydrochloric acid. The mixture is extracted with ethyl acetate (3 x 500 ml) and the organic fractions are combined, washed with brine, then dried over anhydrous sodium sulphate. The mixture is filtered and the filtrate is evaporated under reduced pressure. The residue is purified by column chromatography on silica gel to give 4-bromo-2- ethylphenylboronic acid (26 g) as a white solid.
Step 2: Preparation of 4-bromo-2,6-diethylphenylboronic acidTo a solution of 4-bromo-2,6-diethyl-1-iodobenzene (1O g, 0.029 mol) in tetrahydrofuran (100 ml) at -75 °C is added n-butyl lithium (1.6 M in hexanes, 22.2 ml, 0.035 mol) dropwise maintaining the temperature of the reaction mixture below -70 0C. When the addition is complete the mixture is stirred at -75 °C for an additional 30 minutes and then trimethyl borate (17.98 g, 0.17 mol) is added dropwise. After the addition is complete the reaction is stirred at -75 0C for 1 hour, then allowed to come to room temperature and stirred for 2 hours, followed by cooling in an ice bath and acidification with 0.5 N aqueous hydrochloric acid. The mixture is extracted with ethyl acetate (3 x 300 ml) and the organic fractions are combined, washed with brine, dried over anhydrous sodium sulphate. The mixture is filtered and the filtrate is evaporated under reduced pressure. The residue is purified by column chromatography on silica gel to give 4-bromo-2,6- diethylphenylboronic acid ( 5 g) as a white solid.
With isopropylmagnesium chloride; In tetrahydrofuran; at -15 - 25℃; for 3h;Inert atmosphere;
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Example R: Preparation of 4-bromo-2-ethylbenzaldehydeTo a solution of <strong>[175278-30-5]4-bromo-2-ethyl-1-iodobenzene</strong> (75 g, 0.24 mol) in tetrahydrofuran (375 ml) at - 75 0C is added n-butyl lithium (1.6 M in hexanes, 196 ml, 0.31 mol) dropwise, maintaining the temperature of the reaction mixture below -70 °C. When the addition is complete the mixture is stirred at -75 0C for an additional 30 minutes and then lambda/,lambda/-dimethylformamide (70.7 g, 0.97 mol) is added dropwise. After the addition is complete the reaction is stirred at -75 °C for 2 hours, then allowed to warm to room temperature for 2 hours. The mixture is cooled in an ice bath and acidified with 0.5 N aqueous hydrochloric acid. The mixture is extracted with ethyl acetate (3 x 500 ml) and the organic fractions are combined, washed with brine, and dried over anhydrous sodium sulphate. The mixture is filtered and the filtrate is evaporated under reduced pressure. The residue is purified by column chromatography on silica gel to give 4-bromo-2- ethylbenzaldehyde (48 g) as an oil.
Step 1: Preparation of 4-bromo-2-ethyl-1-iodobenzene <n="166"/>To a stirred mixture of 4-bromo-2-ethylaniline (80 g, 0.4 mol) in distilled water (400 ml) is added concentrated sulphuric acid (80 ml), followed by brief heating to 60 0C for 1 hour until dissolution is complete. The mixture is allowed to cool to room temperature then further cooled to approximately 0 0C in an ice/salt bath. To this slurry is added an aqueous solution of sodium nitrite (28 g, 0.4 mol) in distilled water (140 ml) dropwise over 15 minutes, maintaining the temperature below 5 0C, followed by additional stirring for 30 minutes. The reaction mixture is allowed to come to room temperature and then a solution of aqueous potassium iodide (199 g, 1.2 mol) in distilled water (200 ml) is added dropwise at room temperature. After the addition is complete the solution is briefly heated to 80 0C then allowed to cool to room temperature again. The reaction mixture is extracted with ethyl acetate (1000 ml x 3) and the organic phase is washed with 1M aqueous hydrochloric acid (500 ml) and aqueous sodium thiosulfate (2 x 250 ml). The organic phase is dried over anhydrous sodium sulphate, filtered and the filtrate is concentrated under reduced pressure. The residue is purified by column chromatography on silica gel to give 4-bromo-2-ethyl-1-iodobenzene (84.6 g) as an orange liquid.
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