6-Azapurines. Part 1. Determination of the tautomeric populations in 3-methylthioimidazo[4,5-e]-as-triazine by 13C and 15N nuclear magnetic resonance spectroscopy
Abstract
3-Methylthioimidazo[4,5-e]-as-triazine (1) was synthesized via ring closure of 5,6-diamino-3-methylthio-as-triazine. By using carbon-13 and nitrogen-15 chemical shifts and three-bond 13C–1H spin–spin coupling constants, the prototropic tautomerism in the imidazole moiety of this 6-azapurine was investigated. The data from these spectral techniques indicated that the 5H-tautomeric form predominates (69%). A critical evaluation of the three methods is provided.