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The University of Southampton
Chemistry

Research project: Harrowven: Radical Reactions

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Synthesis of Helicenes, Aza-helicenes and PhenanthrenesOur pioneering work on the addition of radical intermediates to arenes and heterocycles has been recognised by the International Heterocycles Group with a Special Topic review in Progress in Heterocyclic Chemistry.

We have shown that ortho -additions of aryl radical intermediates to proximal aromatic and heterocyclic ring systems are often efficient and synthetically useful processes giving access to a host of polyaromatic and condensed heterocyclic ring systems. A striking example is our short and high yielding helicene synthesis which uses a tandem radical cyclisation to construct the distorted polyaromatic ring system.

 

Rapid and efficient synthesis of [5]helicenes
Scheme:
plan and elevation views
X-ray of 2,3,7,8,12,13-dimethoxy[7]

 

 


 


It is interesting to note that there are 8 distinct species within the unit cell of 2,3,7,8,12,13-hexamethoxy[5]helicene, with the (M)- and (P)-enantiomers each having four conformational forms (distinguished by colour in the following Figure).

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Figure. X-ray of 2,3,7,8,12,13-dimethoxy[7]helicene - plan and elevation views

 

 

 

Our synthetic route to helicenes exploits some newly uncovered co-operative ortho-effects to control alkene geometry in a double Wittig reaction. It also extends to phenanthrenes, azahelicenes and higher helicenes.

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Scheme. Synthesis of phenanthrenes, azahelicenes and [7]helicenes.

 

 

 

 

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Figure. X-ray of 9,10-dimethoxy[7]helicene - plan and elevation views.

Related research groups

Organic Chemistry: Synthesis, Catalysis and Flow
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