Aminopyrazines acylation

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 N-acylation of a primary or secondary aminopyrazine or of a piperazine (at ring-NH) may be carried out for a variety of reasons, one of which is for subsequent intramolecular cyclization. The following examples illustrate the process of acylation (in the widest sense) and a few typical cyclizations ... 

Amino-1,2,5-thiadiazole is, not unexpectedly, a weak base, exhibiting a pX in water of 2.90. The pK of the iso-7r-electronic compound, 2-aminopyrazine, is 3.14. Aminothiadiazole behaves normally in acylation reactions and acetyl, benzoyl, carbamoyl, and... 

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