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由NADH和蓝光促进的脱碳化合

  • 0Department of Organic Chemistry, Arrhenius laboratory, Stockholm University, 10691 Stockholm Sweden.

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Vicinal Diols via Reductive Coupling of Aldehydes or Ketones: Pinacol Coupling Overview 01:27

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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 on...

Aryldiazonium Salts to Azo Dyes: Diazo Coupling 01:11

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The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the para...

Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction 01:22

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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...

Alkynes to Carboxylic Acids: Oxidative Cleavage 02:01

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Alkynes undergo oxidative cleavage in the presence of oxidizing reagents like potassium permanganate and ozone. The triple bond — one σ bond and two π bonds — is completely cleaved, and the alkyne is oxidized to carboxylic acids. When warm and basic aqueous potassium permanganate is used as an oxidizing agent, alkynes are first converted to carboxylate salts via an unstable α-diketone intermediate. Further, a mild acid treatment protonates the carboxylate anions...

Carboxylic Acids to Methylesters: Alkylation using Diazomethane 01:33

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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...

Aldol Condensation with β-Diesters: Knoevenagel Condensation 01:27

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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...