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In organic chemistry, alkynylation is an addition reaction in which a terminal alkyne (−C≡CH) is added to a carbonyl group (C=O) to form an α-alkynyl alcohol (R 2 C(−OH)−C≡C−R). [1] [2] When the acetylide is formed from acetylene (HC≡CH), the reaction gives an α-ethynyl alcohol. This process is often referred to as ethynylation.
The second step of the reaction to convert dibromoolefins to alkynes is known as Fritsch–Buttenberg–Wiechell rearrangement. 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
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.
Multiple carbon–carbon bond are replaced by carbonyl (C=O) groups, such as aldehydes, ketones, and carboxylic acids. The reaction is predominantly applied to alkenes, but alkynes and azo compounds are also susceptible to cleavage. The outcome of the reaction depends on the type of multiple bond being oxidized and the work-up conditions. [1]
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]
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
In commercial applications, the alkylating agents are generally alkenes, some of the largest scale reactions practiced in industry.Such alkylations are of major industrial importance, e.g. for the production of ethylbenzene, the precursor to polystyrene, from benzene and ethylene and for the production of cumene from benzene and propene in cumene process:
The Seyferth–Gilbert homologation is a chemical reaction of an aryl ketone 1 (or aldehyde) with dimethyl (diazomethyl)phosphonate 2 and potassium tert-butoxide to give substituted alkynes 3. [1] [2] Dimethyl (diazomethyl)phosphonate 2 is often called the Seyferth–Gilbert reagent. [3] The Seyferth–Gilbert homologation