Keele Research Repository

Brief treatment of tetrahydro-4-oxoisoxazolo [2,3-a]
pyridinium bromide and its 3-methyl derivative with boiling acetic anhydride gave 4-acetyl-5,6-dihydro-4H-furo [3,2-b] pyrid-2-one and its 3-methyl counterpart.
The structures of these rearrangement products have been proved by complete hydrogenation, spectroscopy and X-ray diffraction studies. The 2-methylisoxazolo [ 2,3-a ]
pyridinium salt did not undergo the rearrangement; this
suggests a keten or an isoxazoline intermediate.
When 4,5,6,7-tetrahydro-4-hydroximinoisoxazolo [2,3-a] pyridin1um bromide or chloride were heated with acetic anhydride, rearrangement to 4-acetyl-7-halogeno-5,6-dihydro-4H-pyrrolo [3,2-b] pyrid-2-one occurred. Mechanisms for the rearrangement have been suggested.
Photolysis of the rearrangement products led to the isolation of dimers. Photolysis of 5,6-dihydro-4H-furo
[3,2-b] pyrid-2-one gave a dimer when using benzene as the solvent; when methanol was used 4-hydroxy-3-methoxymethylamino-hexa-2,4-dienoic acid lactone was produced.