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Prototropic Tautomerism of Heteroaromatic Compounds: IV. Five-Membered Rings with Two or More Hetero Atoms

1963; Elsevier BV; Linguagem: Inglês

10.1016/s0065-2725(08)60746-1

1557-8429

Alan R. Katritzky, J. M. Lagowski,

Synthesis and biological activity

The tautomerism of compounds with five-membered rings and two or more heteroatoms is more complex than that which occurs when only one heteroatom is present. Hydroxy, mercapto, and amino compounds can be in tautomeric equilibrium with oxo, thiocarbonyl, and imino compounds, in which the proton has moved either to an annular nitrogen atom or to an annular carbon atom. The relative position of a functional group with respect to the heteroatoms determines the tautomeric nature of these compounds. Compounds with the same relative orientation of functional group such as hetero atoms-1,3 and hetero atoms-1,2, as well as a potential 4-hydroxyl group—isoxazoles with pyrazoles—are considered in the chapter. All triazoles, tetrazoles, and unsymmetrically substituted imidazoles and pyrazoles can exist in two tautomeric forms. Tautomerism can occur even in the absence of functional groups. Compounds with potential N-oxide groups and potential methyl or substituted methyl compounds are also discussed.