Favorskii reaction
The Favorskii reaction is an
Alexei Yevgrafovich Favorskii.[1]
When the carbonyl is an
enone, although the secondary propargylic alcohol can be isolated in some cases.[2] When this rearrangement is catalyzed by an acid, it is called Meyer–Schuster rearrangement
.
Reaction mechanism and scope
A
metal acetylide is formed in situ when an alkyne is treated with a strong bases such as a hydroxide or an alkoxide:[3]
- HC≡CH + KOH ⇌ HC≡CK + H2O
- RR'C=O + HC≡CK ⇌ RR'C(OK)C≡CH
The metal acetylide then reacts with an aldehyde or ketone to form a
enone.[4]
The applicable
LiOH
fails to form the necessary adduct with alkynes to initiate the reaction.
Hydroxide bases are inexpensive relative to generating an alkoxide or acetylide with reagents such as elemental lithium, sodium, or potassium. Additionally, the stringent reaction conditions used by most alternatives, such as excluding moisture and atmospheric oxygen, are less important, making the reaction easier to perform.[4]
Protecting group
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 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]
See also
- Alkynation
References
- ^ Favorsky, A.E. (1905). "Action of potassium hydroxide on mixtures of ketones and phenylacetylene". Zhurnal Russkago Fiziko-Khimicheskago Obshchestva. 37: 643–645., 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.
- PMID 30250005.
- ^ .
- ^ S2CID 94135082.
- .
- ISBN 9780471697541.