- Derivatives of pyrazinecarboxylic acid: 1H, 13C and 15N NMR spectroscopic investigations
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NMR spectroscopic studies are undertaken with derivatives of 2-pyrazinecarboxylic acid. Complete and unambiguous assignment of chemical shifts (1H, 13C, 15N) and coupling constants (1H,1H; 13C,1H; 15N,1H) is achieved by combined application of various 1D and 2D NMR spectroscopic techniques. Unequivocal mapping of13C,1H spin coupling constants is accomplished by 2D (S,J) long-range INEPT spectra with selective excitation. Phenomena such as the tautomerism of 3-hydroxy-2-pyrazinecarboxylic acid are discussed.
- Holzer, Wolfgang,Eller, Gernot A.,Datterl, Barbara,Habicht, Daniela
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scheme or table
p. 617 - 624
(2010/07/05)
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- Methyl 3-(triphenylphosphoranylideneamino)pyrazine-2-carboxylate: Synthesis, crystal structure and use in pteridin-4(3H)-ones synthesis
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The title iminophosphorane 6 has been prepared from methyl 3-aminopyrazine-2-carboxylate 1 by a modified Kirsanov method using a triphenylphosphine-hexachloroethane-triethylamine system. The crystal structure of 6 illustrated an iminophosphorane function (N=P bond). 2,3-Disubstituted pteridin-4(3H)-ones were obtained in a one-pot reaction of 6 with isocyanates, followed by heterocyclization on addition of alcohols or amines.
- Okawa, Tomohiro,Eguchi, Shoji,Kakehi, Akikazu
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p. 247 - 254
(2007/10/03)
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- Studies on Pyrazines. 29. High Regioselective Synthesis of Chloropyrazines from 3-Substituted Pyrazine 1-Oxides
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Reaction of 3-methoxy- or 3-chloropyrazine 1-oxides with refluxing phosphoryl chloride in the presence of amine led to a high regioselective formation of 3-substituted 2-chloropyrazines.In contrast, the use of chloroacetyl chloride instead of phosphoryl chloride enabled different regioselectivity to yield 6-substituted 2-chloropyrazines, particularly 3-methoxycarbonylpyrazine 1-oxide was almost exclusively converted into methyl 6-chloropyrazinecarboxylate under conditions without the amine.
- Sato, Nobuhiro,Fujii, Megumi
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p. 1177 - 1180
(2007/10/02)
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