三卤化铝脱甲基反应

AlCl₃/CH₃CN和AlBr₃/CH₃CN是【Bull. Chem. Soc. Jpn., 1995, 68, 2033】一类常用的去甲基化方法，其操作类似BBr3的使用，只是一般反应温度在0℃到室温。另外加入硫化物，由于硫的亲核性更强，可以增加反应活性。AlBr3/EtSH,AlCl3/EtSH, AlCl3/HSCH2CH2SH体系的活性很高，分子中酯、醛、酮、双键不稳定，但酯在AlCl3/EtSH/CH2Cl2体系相对稳定。

反应机理

加入硫代物

反应实例

Typical Procedure. To dichloromethane (1 mL) or CH₃CN (1 mL) wasadded aluminum chloride (3.0 mmol) at 0 ℃. Theresulting solution was warmed to room temperature, and the ether (1.0 mmol) wasadded with stirring. After being stirred for 3-12 h, the reaction mixture was pouredinto water, acidified with dilute HC1, and extracted with dichloromethane. Theorganic layer was treated as usual to give a crude product. Chromatography over a silica gelcolumn gave the desired product.

【Y. Kawamura, H.Takatsuki, F. Torii, and T. Horie, Bull. Chem. Soc. Jpn., 1994,67, 511.】

General Procedure for Demethylation.  To a stirredsolution of aluminum halide in ethanethiol cooled in an ice-water bath wasadded the substrate.The reaction was monitored by TLC (aluminum halide was quenched bymethanol in the capillary). The reaction mixture was poured into water,acidified with dilute HC1, and extracted with dichloromethane. The organiclayer was shaken with brine, dried (Na₂SO₄), filtered,and then evaporated to leave a crude material, which was purified bychromatography over a silica gel column.

AlCl₃/EtSH/CH₂Cl₂体系：To a mixture of dry ethanethiol (1 mL) and dichloromethane (1 mL) was added aluminum chloride (0.40 g, 3.0 mmol) at 0 oC. The resulting solution was warmed to room temperature,and the ether (0.194 g,1.0 mmol) was added with stirring. After being stirred for 9.5 h, the reactionmixture was poured into water, acidified with dilute HCl, and extracted with dichloromethane.The organic layer was treated as usual to give a crude product.Chromatography over a silica gel column gave the desired product (0.157 g, 95.5%) identical with anauthentic sample.

AlCl₃/EtSH 体系：To a solutionof aluminum chloride (47 mg, 0.35 mmol) in dry ethanethiol (1 mL) was added the ether (11 mg, 0.03mmol) at 0 oC. After being stirred for 2.5 h at 0 oC, the reactionmixture was poured into water and extracted with dichloromethane. The usual workup of theorganic layer gave the product: 7.5 mg (81.5%). 

【 M. node, K.Nishide, K. Fuji and E. Fujita, J. Org. Chem. 1980, 45, 4275. 】