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Related Concept Videos

Electrophilic Addition to Alkynes: Halogenation02:38

Electrophilic Addition to Alkynes: Halogenation

10.7K
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
10.7K
Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation02:47

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation

22.2K
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.
22.2K
Preparation of Alkynes: Dehydrohalogenation02:34

Preparation of Alkynes: Dehydrohalogenation

19.0K
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.
19.0K
Preparation of Alkynes: Alkylation Reaction02:27

Preparation of Alkynes: Alkylation Reaction

12.9K
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.
12.9K
Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

9.8K
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.
9.8K
Halogenation of Alkenes02:46

Halogenation of Alkenes

21.7K
Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
21.7K

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Updated: Apr 20, 2026

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes
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Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes

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Method for transforming alkynes into (E)-dibromoalkenes.

Jiannan Xiang1, Rui Yuan, Ruijia Wang

  • 1State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University , Changsha, 410082, P. R. China.

The Journal of Organic Chemistry
|November 20, 2014
PubMed
Summary
This summary is machine-generated.

Copper(II) bromide enables a highly stereoselective synthesis of (E)-dibromoalkenes from alkynes. This efficient method uses mild conditions and tolerates various functional groups, making it a versatile tool for organic synthesis.

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Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts
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Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
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Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts
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Area of Science:

  • Organic Chemistry
  • Synthetic Chemistry

Background:

  • Alkyne functionalization is crucial in organic synthesis.
  • Developing stereoselective methods for creating valuable intermediates is an ongoing challenge.

Purpose of the Study:

  • To develop a novel, efficient, and stereoselective method for alkyne bromination.
  • To synthesize (E)-dibromoalkenes using mild reaction conditions.

Main Methods:

  • Utilizing copper(II) bromide as both a reactant and catalyst.
  • Investigating the stereoselectivity of the bromination reaction.
  • Testing the tolerance of various functional groups under the reaction conditions.

Main Results:

  • Achieved highly stereoselective synthesis of (E)-dibromoalkenes.
  • Demonstrated the efficiency of copper(II) bromide as a dual-purpose reagent.
  • Confirmed mild reaction conditions and broad functional group tolerance.

Conclusions:

  • The developed method provides a general and efficient route to (E)-dibromoalkenes.
  • Copper(II) bromide mediated bromination offers a valuable synthetic strategy.
  • The mild conditions and functional group tolerance enhance the applicability of this transformation.