Aryne

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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.

[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 ⁴. 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 ³. The precursor to benzyne in this reaction is 2-(Trimethylsilyl)phenyl triflate.

[edit] See also

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

[edit] References

• ¹ Gilchrist T.C.; Rees C.W.; (1969) Carbenes, Nitrenes and Arynes. Nelson. London.
• ² Organic Syntheses, Coll. Vol. 10, p.678; Vol. 75, p.201 Article
• ³ Facile insertion reaction of arynes into carbon–carbon -bonds Hiroto Yoshida, Masahiko Watanabe, Joji Ohshita and Atsutaka Kunai, Chem. Commun., 2005, (26), 3292 Abstract
• ⁴ Iptycenes, cuppedophanes and cappedophanes Harold Hart Pure & App Chem, Vol. 65, No. 1, pp. 27-34, 1993. Article