Favorskii reaction

The Favorskii reaction (not to be confused with the Favorskii rearrangement), named for the Russian chemist Alexei Yevgrafovich Favorskii , is a special case of nucleophilic attack on a carbonyl group involving a terminal alkyne with acidic protons. [M. Smith, J. March, "March's advanced organic chemistry", Wiley-Interscience, 2001]

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

Reaction mechanism

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 alpha hydrogen is present (as is the case when the carbonyl is an aldehyde), it will tautomerize to the corresponding enone.

This reaction is used as a protect alkynes: the alkyne is either converted with acetone to a 2-hydroxyprop-2-yl-alkyne or converted directly with the commercially available 3-methyl-1-butyne-3-ol also to a protected alkyne. The protective group can be removed by heating the compound in a solution of potassium hydroxide in isopropanol (a retro-Favorskii reaction). [T. Greene, P. Wuts, "Protective groups in organic synthesis", Wiley-Interscience, 1998]

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