选择性还原系列[2] 不脱卤素也不脱O-苄基的硝基还原和烯烃还原方法

前言

铑炭催化下硝基的选择性还原反应：铁钴镍的影响

• 添加剂对反应选择性的影响：
  

追求阅读效率，直接看结果：

在Leimgruber-Batcho吲哚合成反应中，如果没有活化剂，会生成大量的脱苄基产物。

但是，加入3种常见的无机盐，则极大地提高了反应的选择性，尤其是醋酸亚铁。

• 底物拓展：
  

上述方法应用于含O-苄基底物，芳基氯，芳基溴，甚至是还原条件下极易脱卤的芳基碘底物，都能提供良好的选择性。

• 双键的选择性还原：

上述方法还可以用于烯烃的选择性还原，还原烯烃的时候不会脱卤或者脱苄基。

• 其他无机盐对选择性的影响：
  

其他铁钴镍盐，如NiBr2, Ni(acac)2, FeCl2, FeBr2, Fe(OOCCH)2, FeCl3, CoCl2, Co(acac)2 等也可以提供良好的选择性，但上面提到的三种盐结果最好。

• 关键试剂：

• 实验操作：
  

General procedure for hydrogenation. 

To a mixture of enamine 5 (5.00 g, 15.4 mmol), iron(II) acetate (28 mg, 0.154 mmol) and 5% Rh/C (317 mg, 0.154 mmol), tetrahydrofuran (THF) (100 mL) were added. The atmosphere was replaced with N2, followed by H2 and continued at room temperature under a balloon pressure of H2 until the starting enamine 5 and the intermediate 6-benzyloxy-1-hydroxyindole had disappeared. After stirring for 15 h, the atmosphere was replaced with N2 and aqueous NH3 (ca.14%, 20 mL) was added. The following work-up operations were carried out under N2. After stirring for 20 min, the mixture was filtered to remove the catalyst, which was washed with THF (50 mL). The combined mixture was extracted with toluene (50 mL) and the organic layer was washed with aqueous citric acid (10%, 50 g), aqueous sodium bicarbonate (5%, 50 g) and brine (20%, 50 g). The yield of the target indole 4 was determined by HPLC (3.30 assay g, 96% yield).

参考文献：

‍Highly chemoselective reduction using a Rh/C–Fe(OAc)2 system: practical synthesis of functionalized indoles

Tetrahedron Lett.2006, 47, 969. 

doi.org/10.1016/j.tetlet.2005.11.145

注：文中图片可能源于参考文献，若有侵权，请联系删除。