Base Catalyzed Rearrangement of Isoxazolinyl Heterocycles: Synthesis of Annelated Pyrimidines

Abstract

The rearrangement of a number of ethyl 2-(heterocyclic)-5-oxo-2,5-dihydroisoxazole-4-carb-oxylates by mild base is described, leading to new syntheses of the pyrimido [2,1-a] isoquinoline, pyrimido [1,2-a]quinoline, pyrimido [2,1-b] benzothiazole , pyrirnido [1,2-a] pyrimidine, pyrimido [1,2-b]pyridazine and pyrimido [1,2-c] quinazoline ring systems. A mechanism is suggested, and X-ray crystallographic evidence presented for the structure of one of the products, ethyl 2-hydroxy-4-oxo-4H-pyrimido[2,1-a]isoquinoline-3-carboxylate.