3-Amino-5-chloro-1 -methyl-2 pyrazinone

The cycloadducts formed from the Diels-Alder reaction of 3-amino-5-chloro-2(17/)-pyrazinones with methyl acrylate in toluene are subject to two alternative modes of ring transformation yielding either methyl 6-cyano-l,2-dihydro-2-oxo-4-pyridinecarboxylates or the corresponding 3-amino-6-cyano-l,2,5,6-tetrahydro-2-oxo-4-pyridinecarboxylates. From the latter compounds, 3-amino-2-pyridones can be generated through subsequent loss of HCN <96 JOC(61)304>. Synthesis of 3-spirocyclopropane-4-pyridone and furo[2,3-c]pyridine derivatives can be achieved by the thermal rearrangement of nitrone and nitrile oxide cycloadducts of bicyclopropylidene <96JCX (61)1665>. 

Methoxy- 2(1 77)-pyrazinethione 3 -Methoxy- 2(1 77)-pyrazinone 6-Methoxy-2(177)-pyrazinone 2-Methoxy-3-trimethylsilylpyrazine Methyl 6-acetamido-2-pyrazinecarboxylate Methyl 3-acetoxy-2-pyrazinecarboxylate Methyl 5-acetoxy-2-pyrazinecarboxylate Methyl 6-acetoxy-2-pyrazinecarboxylate Methyl 5-acetyl-3-amino-2-pyrazinecarboxylate Methyl 6-acetyl-3,5-diamino-2-pyrazinecarboxylate Methyl 5-allylamino-3-amino-6-chloro-2-pyrazinecarboxylate... 

Another useful method for the elucidation of the hydroxypyrazine-pyrazinone tautomerism is UV spectral analysis. The objective structure in solution is easily estimated by comparison with the UV spectra of the proton-fixed compounds of two tautomers, O-methylated (22) and A-methylated derivatives (23), which are prepared by methylation of the hydroxypyrazines or pyrazinones with diazomethane (Scheme 2). For example, 6-amino-5-benzyl-3-methyl-2(177)-pyrazinone (21 R = Me, R = CHzPh, X = NH2) has been shown to predominate over the hydroxy form (20) because of its nearly identical UV spectrum with the corresponding V-methylated derivative (23) <93JOC7542>. In contrast, 6-chloro-2-hydroxypyrazines (20 R, R = Me or Ph, X = Cl) exist in the hydroxy form rather than as the tautomeric amide, which is an exceptional example of predominance of the hydroxy form with parallels in the chloro-pyridinone field <7UCS(C)2977>. 

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