Chemistry of 3-oxygenated isoxazoles. Formation and X-ray analysis of ethyl (RS)-6-tert-butyl-5-methyl-4-oxo-2,3-dihydro-4H-1,3-oxazine-2-carboxylate, an isoxazol-3(2H)-one rearrangement product

Abstract

Treatment of 5-tert-butyl-4-methylisoxazole-3-ol 8 with ethyl chloroacetate under basic conditions gave ethyl (5-tert-butyl-4-methylisoxazol-3-yloxy)acetate 9 and the unexpected products ethyl (RS)-6-tert-butyl-5-methyl-4-oxo-2,3-dihydro-4H-1,3-oxazine-2-carboxylate 14 and (RS)-2,4,4-trimethyl-3-oxopentanamide 15. The structure of 14 was determined by an X-ray analysis. It is proposed that formation of 14 proceeds through the isoxazol-3-(2H)-one intermediate 10, the acetate carbanion 11 and the dioxo imine intermediate 12. Compound 15, which does not seem to be a degradation product of 14, may be formed by hydrolysis of the dioxo imine 12.