Synthesis and rearrangement of cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-8/9-ones: an access to cycloalkyl[1,2-d]oxazolo[3,2-a]pyrimidin-5-ones

4a-Hydroxycycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-9-ones 2 were synthesized from ethyl 2-oxocyclohexanecarboxylate by an one-step cyclocondensation from the 2-amino-2-oxazolines 1a-c in ethanol at room temperature, and easily dehydrated to provide oxazolo[3,2-a]pyrimidin-9-ones 3. In refluxing xylene, the reaction conducted with various ethyl 2-oxocycloalkanecarboxylates led to the two isomeric oxazolo[3,2-a]pyrimidinones 3 and 4.