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从苯胺的衍生物出发合成吲哚

 从苯胺的衍生物合成吲哚虽不常用,但还是有一些方法被报道。

1 、苯胺经佛克烷基化再还原关环合成吲哚。

       To a stirred solution of boron trichloride (645 mg, 5.5mmol) in dry benzene (6 mL), a solution of 4-chloroaniline 1 (638mg, 5 mmol) in dry benzene (6 mL) was added dropwise under ice-cooling. To the resulting mixture containing 4-chloroaniline borontrichloride complex, chloroacetonitrile (0.38 mL, 6 mmol) and aluminum trichloride (734 mg, 5.5 mmol) were added successively. The mixture was then refluxed for 6 h under nitrogen, becoming a solution of two layers. The evolved hydrogen chloride was absorbed through a drying tube containing silica gel or calcium chloride to a surface of aqueous sodium hydroxide. After cooling, ice 2 N hydrochloric acid was added and a yellow precipitate was formed. To hydrolyze the ketimine of 2 the mixture was warmed at 80 °C under stirring, until the precipitate had dissolved (ca. 30 min). The cooled mixture was extracted with chloromethane (three times) and the organic layer was washed with water, dried (MgS0 4 ), and concentrated. The neutral fraction obtained (744 mg) was recrystallized to obtain pure 2 (674 mg). Yield:

66%. The acidic layer was made alkaline with 2 N sodium hydroxide and extracted with dichloromethane. Washing, drying, and evaporation of the solvent gave the basic fraction (170 mg). Thin-layer chromatographic purification (silica gel, chloroform containing 10% methanol) gave recovered 1 (103 mg).


     To a stirred solution of 5-chloro-2-amino-α-chloroacetophenone 2 (204 mg, l mmol) in dioxane (5 mL) containing water (0.5 mL) was added sodium borohydride (1.1 mmol) and the solution was refluxed for 5.5 h. After removal of the solvent, water was added and the mixture was extracted with dichloromethane. The extract was dissolved in benzene and passed through a silica gel layer (ca. 2 g) to remove a polar fraction. The eluate with benzene was concentrated giving indole 3 (one spot, on TLC, dichloromethane). Yield: 69%

2、 N- 羟基苯胺DMAP 催化下与丙炔酸酯缩合合成 3-羧酸吲哚衍生物

其机理可以理解为如下方式:

      To a solution of N-benzyl-N-phenylhydroxylamine 1 (86.2 mg, 0.426 mmol) in THF (15.0 mL) was added 4A molecular sieves. DMAP (6.0 mg, 0.049 mmol) and methyl propiolate 2 (54mg, 0.562 mmol) were added to it at 0°C. The reaction mixture was stirred at 0°C for 1 h,

then at room temperature for 48 h. Ethyl acetate (5.0 mL) was added, and after filtration, the organic solution was washed with water (3 x 20 mL), brine, and then dried over magnesium sulfate. Following filtration, the organics are concentrated under reduced pressure and the resultant oil purified by flash column chromatography (hexanes: ethyl acetate= 7:3) as eluent to give 1-benzyl-1H-indole-3-carboxylic acid methyl ester 3 (95.6 mg; 82% yield) as a white solid (m.p. 67.0-67.5°C).

3、Nenitzescu 吲哚合成

        Nenitzescu 是一类比较特殊的吲哚合成方法,它的最终产物一般都是在 N 原子上有芳香环的化合物。对于 Nenitzescu 反应而言,最后一步合环反应采用不同的溶剂会得到不同的合环产物。如下的化合物 4 和 5 所示。

      To a solution of (E)3-amino-but-2-enenitrile 1 (1.0 g, 12.2 mmol) in acetic acid (1.54 g, 25mmol) and water (5 mL) was added aniline 2 (1.13 g, 12.2 mol) at r.t.. After stirring for 30min., the mixture was cooled in an ice bath and the product 3 was collected on a filter, dried in vacuum. (The mixture also can be extracted with acetic ether if there was no precipitate appearance.)

     To the solution of 1,4-benzo quinone (0.96 g, 9.0 mmol) in acetic acid (4 mL) was added acetic anhydride (0.8 mL) at r.t.. After stirring for 30 min., a solution of(E)3-Phenylamino-but-2-enenitrile 3 (1.18 g, 7.5 mmol) in acetic acid (4 mL) was added to it and the mixture was stirred overnight. Crude solid was collected after filtered, washed with a little acetic acid and water, dried in vacuum. The solid was purified by column chromatography on silica gel using EtOAc/petro ether (1:2) as eluent to yield 6-hydroxy-3-cynao-2-methyl-1-phenyl-indole 4. (30%)



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