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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.

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.

Electrophilic Addition to Alkynes: Hydrohalogenation

Electrophilic Addition to Alkynes: Hydrohalogenation

Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.

Nucleophilic Aromatic Substitution: Elimination–Addition

Nucleophilic Aromatic Substitution: Elimination–Addition

Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is confirmed through isotopic...

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Related Experiment Video

Updated: May 13, 2026

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Published on: February 16, 2020

Alkane C-H insertion by aryne intermediates with a silver catalyst.

Sang Young Yun¹, Kung-Pern Wang, Nam-Kyu Lee

¹Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, USA.

Journal of the American Chemical Society

|March 13, 2013

Summary

Silver catalysts enable arynes to activate alkane C-H bonds under mild conditions. This efficient C-H functionalization avoids harsh reagents, offering a simpler approach to C-H bond activation.

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Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

Published on: September 18, 2016

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Last Updated: May 13, 2026

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Published on: February 16, 2020

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

Published on: September 18, 2016

Area of Science:

Organic Chemistry
Catalysis
C-H Functionalization

Background:

Traditional transition-metal-catalyzed C-H functionalizations often require harsh conditions, directing groups, oxidants, or bases.
Developing milder and more efficient methods for C-H bond activation remains a significant challenge in synthetic chemistry.

Purpose of the Study:

To investigate the direct activation of alkane C-H bonds using arynes generated from alkyne building blocks.
To explore the use of silver catalysts for promoting this C-H bond functionalization under mild conditions.

Main Methods:

Generation of arynes in situ from alkyne precursors.
Utilizing catalytic amounts of silver complexes to mediate the reaction.
Employing modest heating as the primary energy input.

Main Results:

Arynes, facilitated by silver catalysts, effectively activate primary, secondary, and tertiary alkane C-H bonds.
The reaction proceeds under significantly milder conditions compared to conventional methods, avoiding extra promoters.
Mechanistic studies indicate a concerted C-H bond breaking and new bond formation process, a formal 1,2-addition.

Conclusions:

Silver-catalyzed aryne chemistry provides an efficient and mild route for alkane C-H bond activation.
This method simplifies C-H functionalization by eliminating the need for harsh reagents and directing groups.
The findings offer a valuable new tool for organic synthesis, enabling more accessible C-H bond transformations.