1. Reduction of nitro group

The reduction of nitro group is a common method to synthesize primary amines, especially aromatic primary amines. Generally speaking, the cleanest and easiest reduction method is hydrogenation through Pd / C or Raney Ni, but when there are hydrogenation sensitive functional groups such as halogen (CL, Br and I; When f is insensitive to hydrogenation, double bond and triple bond, we have to adopt chemical reduction method. The most classical method is reduction of iron powder, SnCl2 reduction. In addition, abderahman has reported (synthesis, 1988, 2, 154-155). Although they used alkali in the literature, we found in practice that only a few hours of refluxing in ethanol can be used. This method is also a relatively simple and easy to handle reaction,

Generally speaking, nitro compounds do not need to be reduced by lithium aluminum hydride (LAH), because lah can not completely reduce nitro compounds to obtain mixtures, but for unsaturated conjugated nitro compounds, they can be reduced by lithium aluminum hydride (LAH) reduction or NaBH4 Lewis acid to obtain saturated amines.

2. Reduction of amide

The reduction of amides is also a common method for the synthesis of amines. It is often used for the monoalkylation of primary amines. Generally, the most common way to reduce amides to amines is through the heating and reflux of lah. However, when there are functional groups sensitive to the reduction of lah in the molecule, such as the presence of halogen atoms on the aromatic ring, especially bromine and iodine (in this violent condition, it is easy to cause the dealkylation There are other carboamides in the molecule. Therefore, some mild reduction conditions are needed. At present, the commonly used ones are borane reduction, NaBH4 Lewis acid system reduction, DIBAL reduction, etc. In addition, carboamide can also be reduced to methyl under the reduction condition of lah, which is also a commonly used method of monomethylation of primary amine. Generally, BOC (TERT butoxycarbonyl) is easy to react and the purification of intermediates, so it is often used in such reactions.

3. Reduction of nitriles

Generally, nitrile group is the primary amine, which can be used for catalytic hydrogenation or chemical reduction. Ranney Ni is the most commonly used catalyst for catalytic hydrogenation, When Ranney Ni is used as catalyst to hydrogenate amines, if ethanol is used as solvent, ammonia water is usually added, mainly because under this condition, sometimes a small amount of ethanol will be oxidized to acetaldehyde, which will undergo reductive amination with the product to obtain ethylated product. Adding ammonia water or liquid ammonia can inhibit the side reaction. In chemical reduction, lah and borane are more commonly used.

4. Reduction of azide

Azide reduction is also a commonly used method for the preparation of alkyl primary amines. Generally, alkyl azides are mainly replaced by azides by alkyl halides; alkyl alcohols can also be directly converted to alkyl azides (as if they were primary alcohols) by DPPA. Although a lot of literatures use azido to obtain alkyl azide through the high yield of Mitsunobu with alcohol, because azido is volatile and highly toxic, it is not recommended to be used in the laboratory. For tertiary alcohols, they can also be converted to tertiary alkyl azides by tmsn3 in the presence of Lewis acid.

Both catalytic hydrogenation and chemical reduction can be used for the reduction of azide. Pd / C and Raney Ni are commonly used as catalyst for catalytic hydrogenation. When there are halogen sensitive to hydrogenation in the molecule, PtO2 can be used as catalyst. The most mild condition of chemical reduction is to use triphenylphosphine to reduce in wet tetrahydrofuran, of course, lah can also be used for this reduction.