Synthesis of isomeric isoxazolopyridinones

Reaction of 4-methylamino-5,6-dihydropyridinone with acetyl chloride yielde d exclusively the 3-acetyl derivative. When the methylamino group of the la tter was removed by alkaline hydrolysis, a mixture of two hydroxy derivativ es was formed. Those cyclized upon treatment with hydroxylamine exclusively to the isoxazolo[4,5-c]pyridinone, whereas the 4-methylamino analogue yiel ded, depending on pH, mainly the isoxazolo[4,3-c]pyridinone or the isoxazol o[4,5-c]pyridinone. The configurations of the latter compounds were establi shed by NMR experiments.