4、BX3 和Me2S的絡(luò)合物
BX3 和Me2S的絡(luò)合物為 BBr3 的改良方法。BBr3 或BCl3 和Me2S 的絡(luò)合物是固體物，容易制備并在惰性氣體中能長(zhǎng)期保存。一般使用2 到4 倍量即可。
范例：
Table3. Cleavage of Ethers with BBr3.S(CH2)2 Complex
a) Reaction run at 83°C. b) GLC yield. C) Isoated yield.
General Procedure for the Cleavage of Ethers with Boron Trihalide-Methyl sulfide Complex. To a flame-dried 100 mL flask under an atmosphere of nitrogen is added 1,2-dichloroethane (30 mL) and an amount of boron trihalide-methyl sulfide complex as indicated in Table 3. To this solution is added the desired number of equivalents of the aryl ether. The reaction mixture is stirred at reflux and monitored by either TLC or GLC where convenient. When the starting material disappears, the reaction mixture is hydrolyzed by adding water (30 mL), stirring for 20 min and diluting with ether. The organic phase is separated and washed with 1 M NaHCO and the phenol is subsequently taken up with 1 N NaOH (3×20 mL). The combined NaOH washings are acidified and the product is subsequently extracted into ether, dried (MgSO ) and the solvent is removed in vacuum.
5、BBr3/NaI/15-crown-5
這種體系為比BBr3 更強(qiáng)的去甲基化方法。也可用于脫除烷基甲基醚。
范例：
Table4. Dealkylation of Alkyl Methyl Ethers with BBr3-NaI-15-crown-5
a) Yield of isoated alcohol.
Typical Procedure. Cleavage of 3-Phenylpropanol Methyl Ether.
To a stirred solution of 3-phenylpropanol methyl ether (103 mg, 0.687 mmol) in dry methylene chloride (0.5 mL) is added 0.3 M solution of 15-crown-5 (13.7 mL, 6 equiv.) with NaI in methylene chloride followed by addition of 1 M solution of BBr3 (2.1 mL, 3 equiv.) in methylene chloride at -30°C under argon. The reaction mixture is stirred at the same temperature for 3 hrs, quenched by the addition of saturated aqueous NaHCO3 solution (2 mL) and worked up in the usual manner. Chromatographic purification of the crude product gives the pure alcohol (93 mg,100%), identical in all respects with an authentic sample.
6、Me2BBr
文獻(xiàn)報(bào)道，這個(gè)試劑去甲基化經(jīng)由SN2 機(jī)理，因此，非常有效的只是斷裂C-O 鍵，從而形成酚或醇，不易產(chǎn)生溴代副產(chǎn)物。
范例：
Table5. Cleavage of Ethers with (CH3)2BBr
a) Yield of isoated Product.
Typical Procedure. Cleavage of 1-Methoxydecane. To a cold (0°C), stirred solution of 1-methoxydodecane (1.03 mmol) and triethylamine (0.21 mmol, to neutralize traces of free acid) in dry methylene chloride (4.1 mL) under argon, is added a solution of dimethylboron bromide (1.34 M, 0.99 mL) in methylene chloride. The cooling bath is then removed and the resultant solution is then stirred at room temperature for 3 hrs. The reaction mixture is then cooled to 0°C, quenched with saturated aqueous sodium bicarbonate (2 mL) and diluted with ether (30 mL). The organic layer is separated, washed with saturated sodium bicarbonate (2 mL), water (2 mL) and brine (2 mL). The aqueous washings are extracted with ether and the organic layers are combined. After drying the resultant solution is concentrated and subjected to flash chromatography to provide pure 1-dodecanol (89%).
