The Synthesis of Novel 6,5- and 6,6-Membered Fused Heterocyclic Compounds Derived from Thymine

Novel pyrimido[1,2-a]pyrimidinones 14, 15 and 16 and imidazo[1,2-a] pyrimidinones 19 and 20, designed as conformationally constrained analogues of 1-(3-amino-2-hydroxypropyl)thymine and 1-(2-amino-3-hydroxypropyl)thymine, respective ly, were synthesized by the ring-opening/ ring-closure rearrangement of the corresponding byciclic oxygen-containing amino compounds 12 and 17.