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Electrophilic Aromatic Substitution: Friedel–Crafts Alkylation of Benzene01:17

Electrophilic Aromatic Substitution: Friedel–Crafts Alkylation of Benzene

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Friedel–Crafts reactions were developed in 1877 by the French chemist Charles Friedel and the American chemist James Crafts. Friedel–Crafts alkylation refers to the replacement of an aromatic proton with an alkyl group via electrophilic aromatic substitution. A Lewis acid catalyst such as aluminum chloride reacts with an alkyl halide to form a carbocation. The resulting carbocation then reacts with the aromatic ring and undergoes a series of electron rearrangements before giving the final...
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Limitations of Friedel–Crafts Reactions01:26

Limitations of Friedel–Crafts Reactions

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Several restrictions limit the use of Friedel–Crafts reactions. First, the halogen in the alkyl halide must be attached to an sp3-hybridized carbon for the Friedel–Crafts reactions to occur. Vinyl or aryl halides do not react since the carbocations formed are unstable under the reaction conditions. Second, Friedel–Crafts alkylation is susceptible to carbocation rearrangement, and the major products obtained have a rearranged carbon skeleton. In contrast, the acylium ion is...
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Electrophilic Aromatic Substitution: Friedel–Crafts Acylation of Benzene01:11

Electrophilic Aromatic Substitution: Friedel–Crafts Acylation of Benzene

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The Friedel–Crafts acylation reactions involve the addition of an acyl group to an aromatic ring. These reactions proceed via electrophilic aromatic substitution by employing an acyl chloride and a Lewis acid catalyst such as aluminum chloride to form aryl ketone.
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Conjugate Addition (1,4-Addition) vs Direct Addition (1,2-Addition)01:27

Conjugate Addition (1,4-Addition) vs Direct Addition (1,2-Addition)

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α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic attack via two modes: conjugate or 1,4-addition and direct or 1,2-addition.
Conjugate addition results in a thermodynamically stable product. The reaction retains the stronger C=O bond at the expense of the weaker C=C π bond. The process is slow as the β carbon is less electrophilic than the carbonyl carbon.
Direct addition products are...
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EDTA: Auxiliary Complexing Reagents01:26

EDTA: Auxiliary Complexing Reagents

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EDTA titrations are usually carried out in highly basic conditions, where the fully deprotonated form of EDTA, Y4−, actively complexes with the free metal ions in the solution. Several metal ions precipitate as hydrous oxide (hydroxides, oxides, or oxyhydroxides) under these conditions, lowering the concentration of free metal ions in the solution. For this reason, auxiliary complexing agents or ligands such as ammonia, tartrate, citrate, or triethanolamine are used in EDTA titrations to...
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Alkyl Halides02:45

Alkyl Halides

19.9K
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...
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Negative Additive Manufacturing of Complex Shaped Boron Carbides
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Tryptophan Bioconjugation through Auxiliary Boron-Accelerated, Additive-Free Friedel-Crafts Alkylation.

Chiamaka P Uzoewulu1, Emily C Joyner1, Jamie C Thuan1

  • 1Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, United States.

JACS Au
|January 30, 2026
PubMed
Summary

Researchers developed a novel boron auxiliary approach for additive-free bioconjugation. This method enables efficient labeling of proteins without catalysts, offering a promising alternative to strain-promoted chemistry.

Keywords:
Friedel−Crafts reactionadditive-free bioconjugationboronpeptideproteintrifluoroboratetryptophan

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Area of Science:

  • Chemical Biology
  • Organic Synthesis
  • Bioconjugation Chemistry

Background:

  • Additive-free labeling is crucial for interrogating molecular events in biological systems.
  • Strain-promoted chemistry offers a catalyst-free approach but faces challenges in strained compound synthesis.
  • A need exists for alternative strategies to achieve additive-free bioconjugation.

Purpose of the Study:

  • To develop a new additive-free chemical strategy for bioconjugation.
  • To explore the utility of trifluoroborate as an auxiliary group in Friedel-Crafts alkylation.
  • To enable secondary functionalization of proteins post-labeling.

Main Methods:

  • Investigated trifluoroborate-containing thiophene electrophiles for Friedel-Crafts alkylation.
  • Performed dehydrative alkylation of tryptophan in hexafluoroisopropanol (HFIP).
  • Assessed reactivity in the absence of additional catalysts and additives.
  • Demonstrated secondary functionalization of boron-modified tryptophan residues on proteins.

Main Results:

  • Trifluoroborate variants enabled additive-free Friedel-Crafts alkylation of tryptophan at room temperature.
  • The reaction proceeded efficiently in HFIP without Lewis acids or Brønsted acids.
  • Other functional groups on thiophene electrophiles failed to promote additive-free labeling.
  • The boron moiety remained after conjugation, allowing for subsequent boron-based functionalization.

Conclusions:

  • The boron auxiliary approach provides a versatile and efficient method for additive-free bioconjugation.
  • This strategy offers a valuable alternative to strain-promoted chemistry for protein labeling and modification.
  • The ability for secondary functionalization expands the utility of this method in chemical biology.