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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 + H 2 O; RR'C=O + HC≡CK ⇌ RR'C(OK)C≡CH; The metal acetylide then reacts with an aldehyde or ketone to form a propargyl alcohol.
Grignard reagents of acetylene or alkynes can be used to perform alkynylations on compounds that are liable to polymerization reactions via enolate intermediates. However, substituting lithium for sodium or potassium acetylides accomplishes similar results, often giving this route little advantage over the conventional reaction.
The overall combined transformation of an aldehyde to an alkyne by this method is named after its developers, American chemists Elias James Corey and Philip L. Fuchs. The Corey–Fuchs reaction By suitable choice of base, it is often possible to stop the reaction at the 1-bromoalkyne, a useful functional group for further transformation.
In broad strokes, the mechanism of the reaction is believed to first involve a Mannich-like addition of the alkynylmetal species into the iminium ion formed by condensation of the aldehyde and the secondary amine. This first part of the process is a so-called A 3 coupling reaction (A 3 stands for aldehyde-alkyne-amine
Alkyne metathesis is an organic reaction that entails the redistribution of alkyne chemical bonds. The reaction requires metal catalysts. The reaction requires metal catalysts. Mechanistic studies show that the conversion proceeds via the intermediacy of metal alkylidyne complexes .
The imine can isomerise and the alkyne group is placed at the other available nitrogen alpha position. [11] [12] [13] This reaction requires a copper catalyst. The redox A 3 coupling has the same product outcome but the reactants are again an aldehyde, an amine and an alkyne as in the regular A 3 coupling. [11] [14] [15] [16]
Hydration reaction mechanism from 1-methylcyclohexene to 1-methylcyclohexanol. Many alternative routes are available for producing alcohols, including the hydroboration–oxidation reaction, the oxymercuration–reduction reaction, the Mukaiyama hydration, the reduction of ketones and aldehydes and as a biological method fermentation.
The mechanism for base-catalyzed aldol condensation can be seen in the image below. A mechanism for aldol condensation in basic conditions, which occurs via enolate intermediates and E1CB elimination. The process begins when a free hydroxide (strong base) strips the highly acidic proton at the alpha carbon of the aldehyde.