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Borenium Cations for the Direct Electrophilic Borylation of Arenes

Del Grosso, Alessandro

[Thesis]. Manchester, UK: The University of Manchester; 2013.

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Abstract

A catalytic (in Brønsted superacid) and a stoichiometric process were developed to synthesise aryl boronic esters with boron cations via electrophilic arene borylation. The treatment of CatBX (Cat = catecholate; X = Cl, Br) with the triethyl salt [Et3Si][closo-CB11H6Br6] in arene solvent gave a transient boron electrophile that reacted as a synthetic equivalent of [CatB]+ in intermolecular electrophilic aromatic borylation at 25 °C. The by-product of the reaction was a strong Brønsted acid that was able to catalyse arene borylation using CatBH at high temperature. This catalytic process furnished aryl boronic esters in high yield with H2 as the only by-product. The use of the robust and weakly coordinating anion [closo-CB11H6Br6]- and the electrophile-resistant catecholborane were crucial for the catalytic process. The reaction mixture of R2BCl (R2 = Cat, Cl4Cat, Cl2), aprotic amine and AlCl3 mainly gave a borenium salt [R2B(amine)][AlCl4] which was in equilibrium with neutral species as revealed by NMR spectroscopy and reactivity studies. This reaction mixture was effective for the regioselective borylation, by electrophilic aromatic substitution, of a range of N-heterocycles, thiophenes and anilines at room temperature. The transterification in situ provided the synthetically useful and more stable pinacol boronate esters in excellent isolated yield. This process displayed remarkable functional-group tolerance for a boron based strong Lewis acid with weak bases (for example -NMe2), ether, and halogen groups all compatible. This process represents a new and inexpensive one-pot direct arene borylation methodology for producing pinacol boronate esters.

Additional content not available electronically

Crystallographic Information Files

Bibliographic metadata

Type of resource:
Content type:
Administered thesis
Form of thesis:
Traditional
Type of submission:
Doctoral level ETD - final
Thesis title:
Borenium Cations for the Direct Electrophilic Borylation of Arenes
Degree type:
Doctor of Philosophy
Degree programme:
PhD Chemistry (42 month)
Publication date:
2013-03-10T17:53:59
Institution:
The University of Manchester
Location:
Manchester, UK
Total pages:
246
Abstract:
A catalytic (in Brønsted superacid) and a stoichiometric process were developed to synthesise aryl boronic esters with boron cations via electrophilic arene borylation. The treatment of CatBX (Cat = catecholate; X = Cl, Br) with the triethyl salt [Et3Si][closo-CB11H6Br6] in arene solvent gave a transient boron electrophile that reacted as a synthetic equivalent of [CatB]+ in intermolecular electrophilic aromatic borylation at 25 °C. The by-product of the reaction was a strong Brønsted acid that was able to catalyse arene borylation using CatBH at high temperature. This catalytic process furnished aryl boronic esters in high yield with H2 as the only by-product. The use of the robust and weakly coordinating anion [closo-CB11H6Br6]- and the electrophile-resistant catecholborane were crucial for the catalytic process. The reaction mixture of R2BCl (R2 = Cat, Cl4Cat, Cl2), aprotic amine and AlCl3 mainly gave a borenium salt [R2B(amine)][AlCl4] which was in equilibrium with neutral species as revealed by NMR spectroscopy and reactivity studies. This reaction mixture was effective for the regioselective borylation, by electrophilic aromatic substitution, of a range of N-heterocycles, thiophenes and anilines at room temperature. The transterification in situ provided the synthetically useful and more stable pinacol boronate esters in excellent isolated yield. This process displayed remarkable functional-group tolerance for a boron based strong Lewis acid with weak bases (for example -NMe2), ether, and halogen groups all compatible. This process represents a new and inexpensive one-pot direct arene borylation methodology for producing pinacol boronate esters.
Additional digital content not deposited electronically:
Crystallographic Information Files
Keyword(s):
Thesis main supervisor(s):
Funder(s):
Degree grantor:
Language:
en

Institutional metadata

University researcher(s):
Academic department(s):

Record metadata

Manchester eScholar ID:
uk-ac-man-scw:189470
Created by:
Del Grosso, Alessandro
Created:
10th March, 2013, 17:53:59
Last modified by:
Del Grosso, Alessandro
Last modified:
10th April, 2013, 11:11:09

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