Benzynes hetarynes

Aryl thioethers s. Thioethers, ar. Arylthiomethylation 26,844 Aryl tridiloromethyl carbinols -, reactions with nucleophiles, review 22, 629 suppl. 26 Arynes s. Benzyne..., Hetarynes Ascaiite 11,963 suppl. 28 Asscher-Yofsi reaction 21,642 Assistance, intramolecular s. Neighboring group participation... 

Despite the fact that the history of hetarynes is older than that of the benzynes (cf. 2), physical data on these compounds are scarce. Numerous trapping experiments furnished evidence for the formation of brradicaloid intermediates in the field of five-membered heterocycles (didehydrofurans, -thiophenes, and -pyrroles)." Direct spectroscopic data on these species, however, do not exist, which may be attributable to the increased ring strain in the five-membered o-arynes, associated with a strong tendency to undergo ring-opening reactions. 

Very strong bases such as NaNH2 convert unactivated aryl halides into benzyne intermediates which react rapidly with nucleophiles to form the products of an apparently simple nucleophilic substitution. It is now clear that hetarynes are frequent intermediates in reactions of not too highly activated heteroaromatic halides. 

Arynes and hetarynes (heterocyclic arynes)67-72 such as 25 and 26 are named benzyne or dehydrobenzene and 3,4-pyridyne or 3,4-dehydropyridine, respectively. 

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