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ortho–para-Directing Deactivators: Halogens

ortho–para-Directing Deactivators: Halogens

Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...

Alkyl Halides

Alkyl Halides

Structural Properties
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
Unlike alkyl halides, compounds in which a halogen atom is bonded to an sp2 -hybridized carbon atom of a carbon-carbon double bond (C=C) are called vinyl halides. Whereas aryl...

Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene

Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene

Bromination and chlorination of aromatic rings by electrophilic aromatic substitution reactions are easily achieved, but fluorination and iodination are difficult to achieve. Fluorine is so reactive that its reaction with benzene is difficult to control, resulting in poor yields of monofluoroaromatic products. To address this, Selectfluor reagent is used as a fluorine source in which a fluorine atom is bonded to a positively charged nitrogen.

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.

Reactions at the Benzylic Position: Halogenation

Reactions at the Benzylic Position: Halogenation

Benzylic halogenation takes place under conditions that favor radical reactions such as heat, light, or a free radical initiator like peroxide.

Oxidation of Phenols to Quinones

Oxidation of Phenols to Quinones

In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox...

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Updated: Mar 24, 2026

Biosynthesis of a Flavonol from a Flavanone by Establishing a One-pot Bienzymatic Cascade

Biosynthesis of a Flavonol from a Flavanone by Establishing a One-pot Bienzymatic Cascade

Published on: August 14, 2019

Recent structural modification in halogenated flavonoids: a review.

Yunjie He¹, Zhao Zhao¹, Xianheng Wang²

¹Pharmacy School, Zunyi Medical University, Zunyi, China.

Natural Product Research

|March 23, 2026

Summary

This summary is machine-generated.

Halogenation enhances the biological activity of natural flavonoids, showing promise for developing new drugs. This review covers recent advances in modifying flavonoids with halogens for medicinal applications.

Keywords:

Halogenated flavonoids biological activity synthesis and modification

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Qualitative Identification of Carboxylic Acids, Boronic Acids, and Amines Using Cruciform Fluorophores

Published on: August 19, 2013

Area of Science:

Natural Product Chemistry
Medicinal Chemistry
Pharmacology

Background:

Flavonoids are plant-derived compounds with significant anti-inflammatory, anti-tumor, and anti-oxidation properties.
These natural products are utilized across food, medicine, and various industries.
Modification of natural compounds is a key strategy in drug discovery.

Purpose of the Study:

To review recent advancements in the halogenation modification of natural flavonoids.
To summarize the enhanced biological activities of halogenated flavonoids.
To provide a reference for developing novel halogenated flavonoid-based drugs.

Main Methods:

Literature review of scientific publications on flavonoid halogenation.
Analysis of studies reporting biological activities of modified flavonoids.
Synthesis and characterization of halogenated flavonoid derivatives (as reported in literature).

Main Results:

Halogenation significantly boosts the anti-inflammatory, anti-tumor, and anti-oxidation effects of flavonoids.
Specific halogenation patterns correlate with increased potency and altered activity profiles.
Emerging evidence supports the therapeutic potential of these modified compounds.

Conclusions:

Halogenated flavonoids represent a promising class of compounds for pharmaceutical development.
Further research into structure-activity relationships can optimize drug design.
This review highlights the potential of halogenation as a strategy to enhance flavonoid efficacy.