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The Wolff–Kishner reduction is a reaction used in organic chemistry to convert carbonyl functionalities into methylene groups. [1] [2] In the context of complex molecule synthesis, it is most frequently employed to remove a carbonyl group after it has served its synthetic purpose of activating an intermediate in a preceding step.
Mechanism of Wolff-Kishner reduction Aromatic carbonyls are more readily reduced to their respective alkanes than aliphatic compounds. [ 26 ] For example, ketones are reduced to their respective alkyl benzenes by catalytic hydrogenation [ 27 ] [ 28 ] or by Birch reduction [ 29 ] under mild conditions.
Wolff–Kishner reduction: Alkane: If an aldehyde is converted to a simple hydrazone (RCH=NHNH 2) and this is heated with a base such as KOH, the terminal carbon is fully reduced to a methyl group. The Wolff–Kishner reaction may be performed as a one-pot reaction, giving the overall conversion RCH=O → RCH 3. Pinacol coupling reaction: Diol
The Huang modification is a one-pot shortcut for the Wolff-Kishner reduction, a reaction in which ketone and aldehyde carbonyls are converted to the corresponding methylene or methyl groups via the hydrazone derivative.
Hydrazones are intermediates in the Wolff–Kishner reduction. Hydrazones are reactants in hydrazone iodination, the Shapiro reaction, and the Bamford–Stevens reaction to vinyl compounds. Hydrazones can also be synthesized by the Japp–Klingemann reaction via β-keto acids or β-keto-esters and aryl diazonium salts.
The 4-acetyl group could easily be converted to a 4-ethyl group by Wolff-Kishner reduction (hydrazine and alkali, heated); hydrogenolysis, or the use of diborane. Benzyl or tert-butyl acetoacetates also work well in this system, and with close temperature control, the tert-butyl system gives a very high yield (close to 80%). [10]
In organic chemistry, the Schmidt reaction is an organic reaction in which an azide reacts with a carbonyl derivative, usually an aldehyde, ketone, or carboxylic acid, under acidic conditions to give an amine or amide, with expulsion of nitrogen.
The acylated reaction product can be converted into the alkylated product via a Clemmensen or a Wolff-Kishner reduction. [17] The Gattermann–Koch reaction can be used to synthesize benzaldehyde from benzene. [18] The Gatterman reaction describes arene reactions with hydrocyanic acid. [19] [20]