Heteroaromatic tautomerism—general

Elguero, I., Katritzky, A. R., Denisko, O. V., Phototropic Tautomerism of Heterocycles Heteroaromatic Tautomerism—General Overview and Methodology, 76, 1. 

Tlie first two chapters in this volume continue the survey of heteroaromatic tautomerism that was the topic of Volume 76 of Advances in Heterocyclic Chemistry. Tliis whole subject was first dealt with comprehensively in Volumes 1 and 2 of our series, which date back to 1963 and 1964.Tlie area was updated in a special supplementary volume of the series that appeared in 1976 but is now seriously out of date. Tire chapters in Volume 76 deal with a general introduction and the tautomerism of tive-membered monocyclic rings systems. 

Katritzky, A. R., Lagowski, J. M., Prototropic Tautomerism of Heteroaromatic Compounds. /. General Discussion and Methods of Study, 1, 311 //. Six-Membered Rings, 1, 339 HI. Five-Membered Rings and One Hetero Atom, 2, 1 IV. Five-Membered Rings with Two or More Hetero Atoms, 2, 27. 

In many cases, substituents linked to a pyrrole, furan or thiophene ring show similar reactivity to those linked to a benzenoid nucleus. This generalization is not true for amino or hydroxyl groups. Hydroxy compounds exist largely, or entirely, in an alternative nonaromatic tautomeric form. Derivatives of this type show little resemblance in their reactions to anilines or phenols. Thienyl- and especially pyrryl- and furyl-methyl halides show enhanced reactivity compared with benzyl halides because the halogen is made more labile by electron release of the type shown below. Hydroxymethyl and aminomethyl groups on heteroaromatic nuclei are activated to nucleophilic attack by a similar effect. 

General accounts of prototropic tautomerism have been presented by Ingold and Baker" these include an outline of the historical development of the subject in which heteroaromatic compounds are discussed incidentally, and, therefore, such a historical account will not be given here. Of historical interest are Eistert s book on tautomerism and mesomerism which was published in 1938, a review on — NH-CO— tautomerism by Arndt and Eistert published in 1938, and Heller s account of heterocyclic tautomerism which appeared in 1925. Although more recent works on heterocyclic chemistry (e.g., references 9-11) have dealt incidentally with tautomerism, no unified... 

Prototropic Tautomerism of Heteroaromatic Compounds I, General Discussion and Methods of Study... 

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