Favorskii reaction

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Not to be confused with Favorskii rearrangement.

The Favorskii reaction is the nucleophilic attack of a terminal alkyne with acidic protons on a carbonyl group.[1] The reaction was discovered in the early 1900s by the Russian chemist Alexei Yevgrafovich Favorskii.[2][3]

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.[4] 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.

This reaction is used to protect alkynes: the alkyne is either converted with acetone to a 2-hydroxyprop-2-yl-alkyne or a protected alkyne can be directly synthesized using the commercially available 2-methyl-3-butyn-2-ol as an the alkyne source.[5] The protective group can be removed by heating the compound in a solution of potassium hydroxide in propan-2-ol (a retro-Favorskii reaction).[6]

References

  1. ↑ M. Smith, J. March, March's advanced organic chemistry, Wiley-Interscience, 2001
  2. ↑ Favorsky, A.E. (1905). "Action of potassium hydroxide on mixtures of ketones and phenylacetylene". Zhurnal Russkago Fiziko-Khimicheskago Obshchestva 37: 643–645. 
  3. ↑ Favorsky, A.E. (1907). "Action de la potasse caustique sur les mélanges des cétones avec le phénylacétylène". Bulletin de la Société Chimique de France 2: 1087–1088. 
  4. ↑ Ziegenbein, W.; Viehe, H. G. (ed.) (1969). "Chapter 3: Synthesis of Acetylenes and Polyacetylenes by Substitution Reactions". Chemistry of Acetylenes. Marcel Dekker. pp. 169–263. 
  5. ↑ Kukula, H.; Veit, S.; Godt, A. (1999). "Synthesis of Monodisperse Oligo(para-phenyleneethynylene)s Using Orthogonal Protecting Groups with Different Polarity for Terminal Acetylene Units". European Journal of Organic Chemistry 1999 (1): 277–286. doi:10.1002/(SICI)1099-0690(199901)1999:1<277::AID-EJOC277>3.0.CO;2-R. 
  6. ↑ T. Greene, P. Wuts, Protective groups in organic synthesis, Wiley-Interscience, 1998
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