Structural studies on 6‐methyl‐9‐carbamoyl‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones by 1H, 13C and 15N NMR spectroscopy

Gábor Tóth, Carlos de La Cruz, I. Bitter, I. Hermecz, Béla Pete, Zoltán Mészáros

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Abstract

Several 6‐methyl‐9‐carbamoyltetrahydro‐4H‐pyrido[1,2‐α]pyrimidin‐4‐ones have been prepared using phosgene iminium chloride. These compounds can exist in equilibrium as the cis (3A) imine ⇌ (3B) enamine ⇌ trans (3C) imine. 1H, 13C and 15N NMR prove that the cis‐ and trans‐imine isomers are predominant in the equilibrium. 1H NMR data reveal that the share of the 3B enamine form is negligible at measurable concentrations. The isomeric ratio 3A:3C is time dependent and can be monitored by measuring the CH3C‐6 and (CH3)2N signals. The 13C NMR data show that doublets in the range 42–45 ppm for C‐9 are only compatible with the imine forms 3A and 3C. The SCS values of the CH3C‐6 and OCN(CH3)2 groups were calculated and used for identification of the cis and trans isomers. 15N NMR data show that the N‐1 chemical shift of the imine is approximately − 140 ppm for compound 3, whereas that of a fixed enamine is around − 267.8. This provides additional support for the predominance of the imine tautomers in the equilibrium 3A ⇌ 3B ⇌ 3C. 15N data allow the stereoisomers 3A and 3C to be distinguished.

Original languageEnglish
Pages (from-to)229-234
Number of pages6
JournalMagnetic Resonance in Chemistry
Volume20
Issue number4
DOIs
Publication statusPublished - 1982

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Imines
Nuclear magnetic resonance spectroscopy
Nuclear magnetic resonance
Isomers
Phosgene
Chemical shift
Stereoisomerism
Chlorides

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)

Cite this

Structural studies on 6‐methyl‐9‐carbamoyl‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones by 1H, 13C and 15N NMR spectroscopy. / Tóth, Gábor; de La Cruz, Carlos; Bitter, I.; Hermecz, I.; Pete, Béla; Mészáros, Zoltán.

In: Magnetic Resonance in Chemistry, Vol. 20, No. 4, 1982, p. 229-234.

Research output: Contribution to journalArticle

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