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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.

Electrophilic Addition to Alkynes: Halogenation

Electrophilic Addition to Alkynes: Halogenation

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.

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.

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.

Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration

Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration

Introduction
Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.

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Related Experiment Video

Updated: Apr 25, 2026

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

Siloxy alkynes in annulation reactions.

Hui Qian¹, Wanxiang Zhao, Jianwei Sun

¹Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, P. R. China.

Chemical Record (New York, N.Y.)

|August 30, 2014

Summary

Siloxy alkynes are versatile organic synthesis reagents. This review covers their annulation reactions, forming small, medium, and large rings, including lactones, advancing cyclic molecule synthesis.

Keywords:

alkynes annulation cyclization cycloaddition silanes

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Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

Published on: September 8, 2013

Area of Science:

Organic Chemistry
Synthetic Chemistry
Reaction Mechanisms

Background:

Siloxy alkynes are key building blocks in organic synthesis.
Annulation reactions are crucial for constructing cyclic molecules.
Previous methods were limited in ring size and scope.

Purpose of the Study:

To review the annulation reactions of siloxy alkynes.
To highlight the synthesis of diverse carbo- and heterocyclic products.
To showcase recent advancements in synthesizing medium- and large-ring lactones.

Main Methods:

Utilizing siloxy alkynes with various dipolarophiles and reaction partners.
Employing new amphoteric molecules for ring expansion.
Developing novel ring-expansion strategies.

Main Results:

Siloxy alkynes efficiently form three- to six-membered rings.
Successful synthesis of medium- and large-ring lactones achieved.
Demonstrated versatility in creating complex cyclic structures.

Conclusions:

Siloxy alkyne annulation offers practical routes to cyclic compounds.
These reactions provide fundamental insights into siloxy alkyne reactivity.
Expanded scope enables synthesis of diverse and complex cyclic molecules.