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Reduction

There are nitrogen functions in a high oxidation state that can be reduced to give amines.

Oxidation states of carbon and nitrogen in amines, imines, nitriles, amides, oximes and nitro compounds: amines can be obtained by reduction of the more oxidized functions
Reduction of nitro groups: 2,4-dinitrotoluene to 2,4-diaminotoluene with Fe/HCl and 1-nitropropane to 1-propylamine with Zn/HCl

Reduction means taking electrons from another species, which is simultaneously oxidized.

Metals are excellent for this purpose.

The substitution of a good leaving group by cyanide leads to nitriles whose reduction yields amines (with one more carbon).

Synthesis of 3-methylbutylamine: 1-bromo-2-methylpropane with cyanide gives 3-methylbutanenitrile, which is reduced with LiAlH₄

Amides ('with D') give amines ('with N') by reduction:

Reduction of N-methyldodecanamide with LiAlH₄ to N-methyldodecylamine

Ammonia and amines are nucleophiles that could attack aldehydes or ketones. If one introduces a reducing agent in the reaction medium, the intermediate imine is reduced in situ leading overall to a new amine.

YouTube video: preparation of amines by reduction▶ Watch the video on YouTube
Reductive amination: the carbonyl compound and the amine condense to the imine, which is reduced to the new amine