An assay for aryl radicals using BHAS coupling

Aryl radicals are intermediates in many reactions, but determining their presence unambiguously is often challenging. As we recently reported, reaction of 2-iodo-1,3-dimethylbenzene ( 7 ) in benzene with KO t Bu and a suitable organic additive, leads to a base-induced homolytic aromatic substitution...

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Bibliographic Details
Published in:Organic & biomolecular chemistry 2024-01, Vol.22 (5), p.118-122
Main Authors: Clark, Kenneth F, Tyerman, Seb, Evans, Laura, Robertson, Craig M, Murphy, John A
Format: Article
Language:English
Subjects:
Aromatic compounds
Benzene
Biphenyl
Chemical reactions
Coupling
Deuterium
Intermediates
Isotope effect
Isotope studies
Radicals
Substitution reactions
Translocation
Xylene
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Summary:Aryl radicals are intermediates in many reactions, but determining their presence unambiguously is often challenging. As we recently reported, reaction of 2-iodo-1,3-dimethylbenzene ( 7 ) in benzene with KO t Bu and a suitable organic additive, leads to a base-induced homolytic aromatic substitution (BHAS) coupling reaction giving 2,6-dimethylbiphenyl ( 12 ) and biphenyl ( 3 ) as coupled products, together with xylene ( 13 ). In this case, biphenyl arises from a radical translocation and is the major coupling product. This paper now quantitatively investigates that reaction, which shows a very similar ratio for 3  :  12 [ ca. 4 : 1] when using different sources of radical initiation. Deuterium isotope studies provide detailed mechanistic support for the proposed mechanism; when carried out in C 6 D 6 vs . C 6 H 6 , the reaction is characterised by a strong isotope effect for formation of 3 - d 10 vs . 3 , but not for formation of 12 - d 5 vs . 12 . These distinctive properties mean that the transformation can act as an assay for aryl radicals. An advantage of such a BHAS process is its sensitivity, since it involves a chain reaction that can amplify radical activity. An assay for aryl radicals, formed under basic conditions, emerges from the anomalous BHAS chemistry of substrate 7 .
ISSN:1477-0520
1477-0539
DOI:10.1039/d3ob01743e