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Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.

Preparation of Alkynes: Alkylation Reaction

Preparation of Alkynes: Alkylation Reaction

Introduction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.

Preparation of Alkynes: Dehydrohalogenation

Preparation of Alkynes: Dehydrohalogenation

Introduction
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation

Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.

Preparation of Aldehydes and Ketones from Alcohols, Alkenes, and Alkynes

Preparation of Aldehydes and Ketones from Alcohols, Alkenes, and Alkynes

Aldehydes and ketones are prepared from alcohols, alkenes, and alkynes via different reaction pathways. Alcohols are the most commonly used substrates for synthesizing aldehydes and ketones. The conversion of alcohol to aldehyde, which involves the oxidation process, depends on the class of the alcohol used and the strength of the oxidizing agent. For instance, primary alcohol will form an aldehyde when treated with a weak oxidizing agent; however, it gets over-oxidized to a carboxylic acid in...

Reduction of Alkynes to trans-Alkenes: Sodium in Liquid Ammonia

Reduction of Alkynes to trans-Alkenes: Sodium in Liquid Ammonia

Alkynes can be reduced to trans-alkenes using sodium or lithium in liquid ammonia. The reaction, known as dissolving metal reduction, proceeds with an anti addition of hydrogen across the carbon–carbon triple bond to form the trans product. Since ammonia exists as a gas (bp = −33°C) at room temperature, the reaction is carried out at low temperatures using a mixture of dry ice (sublimes at −78°C) and acetone.
When dissolved in liquid ammonia, an alkali metal, such as sodium,...

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Updated: Mar 18, 2026

Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

Published on: June 21, 2017

Direct conversion from alkenes to alkynes.

Junhong Meng^1,2,3, Yiqi Liang^1,2,3, Ruilin Xu^1,2,3

¹State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing, China.

|March 17, 2026

Summary

This summary is machine-generated.

Researchers developed a recyclable selenanthrene reagent for converting alkenes to alkynes under mild conditions. This new method is compatible with sensitive functional groups and allows for stereochemical control, offering a significant advancement over traditional elimination chemistry.

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Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts

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Published on: February 24, 2015

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Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

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Efficient Synthesis of Polyfunctionalized Benzenes in Water via Persulfate-promoted Benzannulation of α,β-Unsaturated Compounds and Alkynes

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Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts

Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts

Published on: February 24, 2015

Area of Science:

Organic Chemistry
Synthetic Chemistry

Background:

Alkynes are crucial in organic chemistry, but their synthesis from alkenes is challenging.
Existing methods rely on harsh elimination chemistry, limiting their use with complex molecules.

Purpose of the Study:

To develop a mild and versatile method for alkene desaturation to alkynes.
To enable late-stage synthesis of complex alkynes and control alkene stereochemistry.

Main Methods:

Utilized a recyclable selenanthrene reagent for alkene desaturation.
Demonstrated compatibility with various leaving groups and sensitive functional groups.

Main Results:

Achieved efficient conversion of alkenes to alkynes under mild conditions.
Enabled stereochemical inversion or sorting of Z/E alkenes, a feat not possible with prior methods.
Showcased broad functional group tolerance for late-stage synthesis.

Conclusions:

The developed selenanthrene reagent offers a mild and efficient alternative for alkyne synthesis.
This method expands synthetic possibilities for complex molecules and stereochemical control.
The reagent's recyclability enhances its practical and sustainable application in organic synthesis.