不用鐵粉，鈀碳，Raney Ni，溫和還原硝基製備胺！

分子科學 2024-02-20 08:12

Raney Ni加氫，但是當分子內存在對加氫敏感的官能團，如：鹵素（Cl, Br and I; F 對加氫不敏感），雙鍵，三鍵時，我們不得不采用其他方法， 最為經典的要數在酸性條件下的鐵粉的還原。含硫的還原劑如硫化鈉、硫化胺、亞硫酸氫鈉、連二亞硫酸鈉等是在堿性或中性條件下選用的還原劑. 此類還原劑的特點是能使多硝基化合物中部分硝基還原為氨基。

2015年，意大利的M. Benaglia團隊報道了HSiCl3作為還原劑在溫和條件下將硝基還原為胺。該方法對很多敏感官能團（如苄基，氰基，鹵素）兼容性良好。此方法芳香硝基化合物和脂肪硝基化合物同樣適用。

對於一些手性硝基化合物，反應後也能保持很好光學活性。

反應機理

HSiCl3和三級胺反應生成SiCl2或[SiCl3]-

兩種可能的機理：

反應操作

General procedure and reaction conditions optimization：In a round bottomed flask the nitro-compound (0.7 mmol) and the tertiary amine (3.5 mmol) were dissolved into the dry solvent (5 mL) under magnetic stirring and nitrogen atmosphere. A solution of freshly distilled HSiCl3 (2.5 mmol) in 2 mL of dry solvent was prepared apart, and it was added drop-wise to the first solution over 10 minutes at 0 °C. After stirring the reaction mixture for 18 h, 5 mL of a saturated solution of NaHCO3 was added drop-wise and the biphasic mixture was allowed to stir for 30 min. The crude mixture was extracted with ethyl acetate, dried over Na2SO4, filtered and then dried under reduced pressure to afford the crude product.

 

參考資料：

Metal-Free Reduction of Aromatic and Aliphatic Nitro Compounds to Amines: A HSiCl3?Mediated Reaction of Wide General Applicability, Org. Lett. 2015, 17, 3941−3943.