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Usually two equivalents of sodium amide yields the desired alkyne. Three equivalents are necessary in the preparation of a terminal alkynes because the terminal CH of the resulting alkyne protonates an equivalent amount of base. Hydrogen chloride and ethanol can also be eliminated in this way, [11] as in the preparation of 1-ethoxy-1-butyne. [12]
A workup step with acid is included to ensure formation of 2-aminopyridine. Reaction progress can be measured by the formation of hydrogen gas and red color from σ-adduct formation. [3] Sodium amide is a handy reagent for the Chichibabin reaction but handling it can be dangerous and caution is advised. [4] σ-adduct (Meisenheimer adduct) formation
The mechanism of this transformation involves the addition of hydride to the carbon less able to stabilize the developing negative charge (viz., in the β position to an electron-withdrawing group). [10] Coordination of aluminium to the resulting trans vinyl carbanion leads to the observed trans configuration of the product. [11] (3)
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
The alkyne zipper reaction requires a strong base, which can be generated from the reaction of potassium hydride and a diamine: [3] [1] Alkyne zipper reaction. The potassium 3-aminopropylamide deprotonates the less-substituted methylene adjacent to the alkyne group. [3] [1] Example mechanism for alkyne zipper reaction.
A 3D model of ethyne (), the simplest alkyneIn organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. [1] The simplest acyclic alkynes with only one triple bond and no other functional groups form a homologous series with the general chemical formula C n H 2n−2.
For instance, oxidation of triphenylphosphine to triphenylphosphine oxide can lead to the formation of Pd 0 in situ when [Pd(PPh 3) 2 Cl 2] is used. Copper(I) salts, such as CuI, react with the terminal alkyne and produce a copper(I) acetylide, which acts as an activated species for the coupling reactions. Cu(I) is a co-catalyst in the reaction ...
In terms of mechanism, the reactions begin with the formation of metal-alkyne complexes. The combination of two alkynes within the coordination sphere affords a metallacyclopentadiene. [ 5 ] Starting from the metallacyclopentadiene intermediate, many pathways can be considered including metallocycloheptatrienes, metallanorbornadienes, and a ...