Aryne

From Wikipedia, the free encyclopedia

In chemistry, an aryne is an uncharged reactive intermediate derived from an aromatic system by removal of two ortho substituents, leaving two orbitals with two electrons distributed between them ^[1]. In analogy with carbenes and nitrenes, an aryne has a singlet state and a triplet state. The name benzyne (1) for the simplest aryne is open for criticism because it implies an alkyne bond which is not the case, a better name is dehydrobenzene. Benzyne is stabilized by resonance between structures 1 and 2 and a more accurate depiction is 3. A suitable chemical trap for benzyne is a cyclopentadiene.

A para-aryne or para-benzyne is a 1,4-diradical species identified in the Bergman cyclization.

Contents 1 Aryne chemistry 2 Scope 3 See also 4 References

[edit] Aryne chemistry

Arynes are prepared from electron deficient aromatic compounds (often aryl halides) in presence of a strong base. The most prominent aryne reactions are Diels-Alder reactions with dienes. Tetrabromobenzene reacts with butyllithium to the diaryne intermediate with furan to form a tetrahydroanthracene ^[2]. The mixture of syn and anti conformers can be separated based on difference in methanol solubility.

Anthracene is converted to a triptycene by Diels-Alder reaction of an aryne with the central benzene ring ^[3]. A pentiptycene is the anthracene analogue after reaction with the diaryne.

Aryne reactivity can also be extended to carbon to carbon insertion reactions into substrates that can react both as a nucleophile and as an electrophile with for instance a malonic acid ester ^[4]. The precursor to benzyne in this reaction is 2-(Trimethylsilyl)phenyl triflate.

[edit] Scope

Aryne chemistry has been applied to the synthesis of novel aryl amines in a tandem reaction including two Diels-Alder reactions with three benzyne molecules reacting to one imidazole molecule ^[5]:

[edit] See also

• More examples use of aryne chemistry: tricyclobutabenzene, in-methylcyclophane

[edit] References