On the mechanism of the generation of 5-oxy-2,3-dihydroimidazo[1,2-a]pyrazin-3-ones by the direct variable-temperature NMR method: a variable-temperature study

Abstract

The mechanism of the generation of 8-benzyl-2-(tert-butyl)-6-(p-methoxyphenyl)-5-oxy- 2,3-dihydroimidazo[1,2-a]pyrazin-3-ones 2a, 2b and 2c from 3-benzyl-2-[1-(2-trimethylsilylethoxycarbonyl)-2,2- dimethylpropylideneamino]-5-(p-methoxyphenyl)pyrazine 1 has been investigated. The structure of an unstable intermediate 4 forming 2a, 2b and 2c in the reactions has been proved to have a 2-(methoxycarbonyloxy)-2,3-dihydroimidazo[1,2-a]pyrazin-3-one ring system by the results of direct variable-temperature ¹ H NMR spectral analysis, low-temperature ¹³ C NMR and 2D NMR ( ¹ H– ¹³ C COSY and COLOC) spectral analysis of the crude reaction mixture.