为了避免醇羟基在直接溴置换反应中可能产生的副反应，可先将醇用磺酰氯转化成为相应的磺酸酯，再与亲核性溴化试剂反应，生成所需的溴化烃。由于磺酰氯及其酯的活性较高，磺酰氯和溴的置换反应均在较温和的条件下进行，且常比溴素交换反应更加有效。常用的溴化剂有溴化钠、溴化锂、溴化镁等。反应溶剂为丙酮、醇、DMF等极性溶剂。

溴化锂作为溴化剂的磺酸酯溴置换反应

In a 500-mL, three-necked,round-bottomed flask equipped with a magnetic stirring bar, reflux condenser, and adropping funnel are placed 20 g (0.23 mol) of 3-methyl-3-buten-1-ol, 160 ml of freshly distilled dichloromethaneand 36 mL (0.24 mol) of triethylamine. The reaction mixture is cooled to −5°C and 14.4 g (0.24 mol) of freshly distilled methanesulfonylchlorideis added dropwise from the dropping funnel. After the reactionmixture is stirred at 0°C foran additional 2 hours, it is quenched with 80 ml of water and the aqueous phaseis extracted three times with 40-mLportions of dichloromethane. The combined organic phase is dried over magnesiumsulfateand the solvent is removed with a rotary evaporator at aspiratorvacuum. The crude yellow oil is taken up in 25ml of dry acetoneand added dropwisefrom a dropping funnel to a slurry of 60 g (0.68 mol) of lithiumbromidein 115 ml of dry acetonein a 250-mL round-bottomed flask fitted with the droppingfunnel and a refluxcondenser. The solution is slowly warmed to 35°C and is stirred at this temperaturefor 18 hours, at which time the reaction is quenched with 120 ml of water. Theaqueous phase is extracted three times with 40ml portions of ether. The combined organic phaseis dried over magnesiumsulfateand the solvent is removed with a rotary evaporator at aspiratorvacuum. The resulting oil is distilled at aspirator pressure to provide 17.7 g (51%) of 4-bromo-2-methyl-1-buteneas a colorless oil: bp 41-42°Cat 34-39 torr.

Ref: Organic Syntheses, Coll.Vol. 10, p.188; Vol. 78, p.202

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