Unprecedented reactivity of 3-amino-1H,3H-quinoline-2,4-diones with urea: an efficient synthesis of 2,6-dihydro-imidazo[1,5-c]quinazoline-3,5-diones

Substituted 3-amino-1H,3H-quinoline-2,4-diones react with urea in acetic acid to give novel 2,6-dihydro-imidazo1,5-c]quinazoline-3,5-diones in high yields. The same compounds were obtained, albeit with small yields, from 3-chloro-1H,3H-quinoline-2,4-diones and urea. In the proposed reaction mechanism, a molecular rearrangement of the primarily formed mono-substituted urea takes place. The prepared 2,6-dihydro-imidazo1,5-c]quinazoline-3,5-diones were characterized by their ¹H, ¹³C, ¹⁵N NMR and IR spectra and atmospheric pressure chemical ionisation mass spectra.