Imine-amine tautomerism

Amine-imine tautomerism in 3-acyl-substituted aminopyrazines has been examined by H, C, and N spectral analysis as well as X-ray crystallography <2005JST67>. In the same way as the parent aminopyrazine, those aminopyrazines have been shown to exist in the amino form 11 (R = H, Me, Ph) (Scheme 2) in contrast to an expectation that the electron-withdrawing acyl groups adjacent to the amino substituent would stabilize the imino tautomers 12 and 13. Thus, all NMR spectra showed only existence of the amino tautomer 11, and additionally the... 

The amine-imine tautomerism, liable to occur in aminopurines which may be illustrated in the particularly important case of adenine by the structures 6 and 7. 

Among the other possible isomeric aminopurines, some attention has been devoted to the amine—imine tautomerism in 2-aminopurine... 

There are various forms of tautomerism which operate in the different purine species. (1) Prototropy which involves attachment of the proton to any one of the four ring nitrogen atoms (Scheme 5). Corresponding CH tautomers, for example (52), seem to be of little significance. (2) Amine-imine tautomerism which operates in the aminopurines such as adenine (Scheme 6). (3) Lactam-lactim tautomerism as in the hydroxypurines such as hypoxanthine (Scheme 7) and the related thioxo-thiol tautomerism (53) and (54) in the biologically imporfant mercaptopurines (Scheme 8). The subject has recently been discussed in some detail <76AHC(Si)502>. 

Under normal conditions, aminooxazoles do not exhibit amine-imine tautomerism. 2-Aminooxazoles have been found to be largely in the... 

Figure 1.64 Illustration of the keto-enol and amine-imine tautomeric equilibria...

Conformational equilibria of amines and aminoacids have been studied in low-temperature matrix under UV or IR irradiation." Amine-imine tautomerism and formation of a radical was observed from adenine. New studies on the aniline excited states has evidenced the role of Rydberg states. A re-examination of the Oilman reaction has demonstrated that this is an electron transfer process. The photo-cyclization of halogenated (iodine is by far to be preferred) N-ben lani-lines to phenanthridine has been studied with particular attention at the preparative value and the tolerance of alko)q, dio)q methylene and halogen substituents, to which it was found to be quite tolerant. ... 

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