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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.

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...

Reduction of Alkenes: Catalytic Hydrogenation

Reduction of Alkenes: Catalytic Hydrogenation

Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...

Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide

Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide

Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.

Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule

Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule

If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...

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.

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Related Experiment Video

Updated: Jul 16, 2025

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

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

Published on: September 12, 2018

Protocol for (E)-selective semihydrogenation of alkynes using iridium-based catalyst.

Rafał Kusy¹, Karol Grela²

¹Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.

|September 21, 2023

Summary

This study presents a new method for (E)-selective alkyne semihydrogenation using an iridium catalyst. The protocol efficiently synthesizes (E)-stilbene with high selectivity and is compatible with various functional groups.

Keywords:

Chemistry Energy Environmental Sciences NMR

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

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Published on: September 8, 2013

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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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Published on: September 12, 2018

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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
Catalysis
Synthetic Methodology

Background:

Alkyne semihydrogenation is crucial for synthesizing alkenes.
Achieving high stereoselectivity, particularly (E)-selectivity, remains a challenge in alkyne transformations.
Development of efficient and selective catalytic systems is essential for organic synthesis.

Purpose of the Study:

To describe a protocol for highly (E)-selective alkyne semihydrogenation.
To provide a method for the synthesis and purification of (E)-stilbene.
To demonstrate the compatibility of the protocol with diverse substrates.

Main Methods:

Utilizing a commercially available iridium complex with a bidentate phosphine ligand.
Performing alkyne semihydrogenation under optimized conditions.
Analyzing the product stereochemistry using gas chromatography (GC) and nuclear magnetic resonance (NMR) spectroscopy.
Purifying the desired (E)-stilbene product via silica gel chromatography.

Main Results:

High (E)-selectivity in alkyne semihydrogenation was achieved.
The protocol successfully synthesized (E)-stilbene.
The method demonstrated compatibility with a broad range of functional groups and alkyne types.
GC analysis confirmed high (Z)/(E) ratios, indicating excellent stereocontrol.

Conclusions:

A robust and efficient protocol for (E)-selective alkyne semihydrogenation has been established.
The developed method offers a reliable route to (E)-stilbene and related compounds.
This protocol is valuable for synthetic chemists requiring stereoselective alkene synthesis.