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Halogenation of Alkenes

Halogenation of Alkenes

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.

Radical Anti-Markovnikov Addition to Alkenes: Overview

Radical Anti-Markovnikov Addition to Alkenes: Overview

The addition of hydrogen bromide to alkenes in the presence of hydroperoxides or peroxides proceeds via an anti-Markovnikov pathway and yields alkyl bromides.

Regioselectivity of Electrophilic Additions-Peroxide Effect

Regioselectivity of Electrophilic Additions-Peroxide Effect

In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.

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...

Formation of Halohydrin from Alkenes

Formation of Halohydrin from Alkenes

An alkene, such as propene, reacts with bromine in the presence of water to yield a halohydrin. Halohydrins contain a halogen and a hydroxyl group attached to adjacent carbons. When the halogen is bromine, it is called a bromohydrin, while a chlorohydrin has chlorine as the halogen.

Regioselectivity and Stereochemistry of Hydroboration

Regioselectivity and Stereochemistry of Hydroboration

A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...

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Related Experiment Video

Updated: May 4, 2026

Efficient Synthesis of All-Carbon Quaternary Centers via the Conjugate Addition of Functionalized Monoorganozinc Bromides

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Published on: May 26, 2019

Stereoselective bromofunctionalization of alkenes.

Chong Kiat Tan¹, Wesley Zongrong Yu, Ying-Yeung Yeung

¹Department of Chemistry, National University of Singapore, Singapore.

|December 17, 2013

Summary

This study explores enantioselective bromocyclization of alkenes and diastereoselective multicomponent reactions using N-bromosuccinimide. It presents novel approaches to stereoselective bromofunctionalization challenges.

Keywords:

alkenes asymmetric catalysis electrophilic addition multicomponent reactions organocatalysis

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Area of Science:

Organic Chemistry
Asymmetric Synthesis

Background:

Stereoselective bromofunctionalization of alkenes is a critical area in organic synthesis.
Enantioselective methods are particularly sought after for creating chiral molecules.
Previous research has laid significant groundwork, as noted in recent reviews.

Purpose of the Study:

To present our group's innovative strategies for enantioselective bromocyclization of alkenes.
To detail the development of diastereoselective N-bromosuccinimide-initiated multicomponent reactions.
To address existing challenges in stereoselective alkene bromination.

Main Methods:

Focus on enantioselective bromocyclization reactions.
Development of multicomponent reactions initiated by N-bromosuccinimide.
Exploration of diastereoselective reaction pathways.

Main Results:

Demonstration of successful enantioselective bromocyclization.
Establishment of novel diastereoselective multicomponent reactions.
Advancement in stereocontrolled bromofunctionalization techniques.

Conclusions:

Our group has made significant contributions to enantioselective bromocyclization.
New diastereoselective multicomponent reactions have been developed.
These findings offer valuable tools for stereoselective synthesis.