Favorskii reaction

The Favorskii reaction is the nucleophilic attack of an acetylide on a carbonyl group.In fact this rearrangement is observed when alpha-halogenoketones are reacted with alkoxide bases(RO-) and forms carboxylic acids and/esters. The reaction was discovered in the early 1900s by the Russian chemist Alexei Yevgrafovich Favorskii.

When catalyzed by acid, this reaction is called the Meyer–Schuster rearrangement.

A metal acetylide is formed in situ when an alkyne is treated with a strong bases such as a hydroxide or an alkoxide:

The metal acetylide then reacts with an aldehyde or ketone to form a propargyl alcohol. When an α-hydrogen is present (as is the case when the carbonyl is an aldehyde), it will tautomerize to the corresponding enone.

The applicable substrates that undergo a Favorskii reaction are limited when compared to the conventional reaction because using an excess of hydroxide base introduces aldol condensation as a more significant competing side reaction. Since enolates do not react with acetylene, the reaction can be often be a poor substitute for the conventional reaction, especially when reaction is used on aldehydes. Successful reactions with aldehydes often require special solvents to be used, such as DMSO or 1,2-dimethoxyethane with a trace amount of ethanol. Additionally, LiOH fails to form the necessary adduct with alkynes to initiate the reaction.

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