State and Explain Wolf Kishner's Reaction
Answers
Answer:
The Wolff-Kishner reduction is an organic reaction used to convert an aldehyde or ketone to an alkane using hydrazine, base, and thermal conditions. The mechanism begins with the attack of hydrazine of the aldehyde or ketone for form an imine. Proton transfer steps then result in the formation of a N=N bond.
Explanation:
The Wolff–Kishner reduction is a reaction used in organic chemistry to convert carbonyl functionalities into methylene groups. 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. As such, there is no obvious retron for this reaction. Originally reported by Nikolai Kischner in 1911[1] and Ludwig Wolff in 1912,[2] it has been applied to the total synthesis of scopadulcic acid B,[3] aspidospermidine[4][5] and dysidiolide.[6]
Scheme 1. Wolff-Kishner Reduction
In general, the reaction mechanism first involves the in situ generation of a hydrazone by condensation of hydrazine with the ketone or aldehyde substrate. Sometimes it is however advantageous to use a pre-formed hydrazone as substrate (see modifications). The rate determining step of the reaction is de-protonation of the hydrazone by an alkoxide base to form a diimide anion by a concerted, solvent mediated protonation/de-protonation step. Collapse of this alkyldiimide with loss of N2 leads to formation of an alkylanion which can be protonated by solvent to give the desired product.
Scheme 1-1. Summary of mechanism of Wolff-Kishner reaction
Because the Wolff–Kishner reduction requires highly basic conditions, it is unsuitable for base-sensitive substrates. In some cases, formation of the required hydrazone will not occur at sterically hindered carbonyl groups, preventing the reaction. However, this method can be superior to the related Clemmensen reduction for compounds containing acid-sensitive functional groups such as pyrroles and for high-molecular weight compounds.
Explanation:
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The Wolff-Kishner reduction is an organic reaction used to convert an aldehyde or ketone to an alkane using hydrazine, base, and thermal conditions. The mechanism begins with the attack of hydrazine of the aldehyde or ketone for form an imine. Proton transfer steps then result in the formation of a N=N bond. Deprotonation of the nitrogen and a rearrangement reaction result in the formation of a carbanion and the release of nitrogen gas. The carbanion then picks up a proton from water to regenerate the base catalyst and provides the final alkane product.
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