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

The mechanism of the generation of benzyl-2-(tert-butyl)6-(p-methoxyph enyl)-5-oxy-2,3 -dihydroimidazo[1,2-a]pyrazin-3-ones 2a, 2b and 2c fro m ethylpropylideneamino]-5-(p-methoxyphenyl)pyrazine 1 has been invest igated, The structure of an unstable intermediate 4 forming 2a, 2b and 2c in the reactions has been proved to have a arbonyloxy)-2,3-dihydro imidazo[1,2-a]pyrazin-3-one ring system by the results of direct varia ble-temperature H-1 NMR spectral analysis, low-temperature C-13 NMR an d 2D NMR (H-1-C-13 COSY and COLOC) spectral analysis of the crude reac tion mixture.