ヴィニリデン炭素センターでのN2/CO交換:1,2,3-トリアゾール由来ディアゾアルケンの安定アルキリデンケテンおよびアルキリデンチオケテン
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Carboxylic acids react with diazomethane in an ether solvent via alkylation at the carboxylate oxygen atom to give methyl esters of the corresponding acid with excellent yields.
Diazomethane is a yellow gas having a boiling point of −23 °C. It is conveniently prepared by the action of a base on N-methyl-N-nitrosourea or N-methyl-N-nitrosotoluenesulphonamide.
The esterification mechanism involves the protonation of diazomethane by the carboxylic acid to yield a carboxylate salt and...
The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.
The reaction is a two-step process. The mechanism is still under study, but for some reagent...
The Claisen rearrangement is a [3,3] sigmatropic rearrangement of allyl vinyl ethers to unsaturated carbonyl compounds. The rearrangement is a concerted pericyclic reaction proceeding via a chair-like transition state.
An aromatic Claisen rearrangement involves the conversion of allyl aryl ethers to an unstable ketone intermediate, which tautomerizes to give ortho-substituted phenols.
However, ortho-substituted allyl aryl ethers exclusively yield para-substituted phenols via two sequential...
The Knoevenagel condensation is an aldol-type reaction involving the condensation of aldehydes or ketones with active methylene compounds such as β-diesters to produce substituted olefins.
The reaction is catalyzed by amine base, which abstracts the acidic α hydrogen of the activated methylene to generate a resonance stabilized enolate ion. The basic strength of the amine is insufficient to form the enolate of aldehydes or ketones. However, it acts as a nucleophile that attacks the carbonyl...
Wilhelm Rudolph Fittig discovered the pinacol coupling reaction in 1859. It is a radical dimerization reaction and involves the reductive coupling of aldehydes or ketones in the presence of hydrocarbon solvent to yield vicinal diols.
The radical reaction is initiated by a single electron transfer from metals like sodium and magnesium to a spin-paired molecule like aldehydes or ketones to generate a ketyl—a radical anion. The ketyl has a radical character on the carbon atom and a charge...
Nitrous acid is a relatively weak and unstable acid prepared in situ by the reaction of sodium nitrite and cold, dilute hydrochloric acid. In an acidic solution, the nitrous acid undergoes protonation when it loses water to form a nitrosonium ion—an electrophile. Nitrous acid reacts with primary amines to give diazonium salts. The reaction is called diazotization of primary amines.
Figure 1. The mechanism of the diazotization reaction of primary amines.
As illustrated in Figure 1, in the...

