Syntheses with isoxazoles. Part IV. Ring-opening reactions of 4,5,6,7-tetrahydro-4-oxoisoxazolo[2,3-a]pyridinium salts and related compounds under the influence of tertiary amines

Abstract

On treatment of the 4,5,6,7-tetrahydro-4-oxoisoxazolo[2,3-a]pyridinium salts (1) and (3) with triethylamine in methanol, methyl 4-(2-formyl-1-methoxyvinylamino)butyrate (7) and its homologue (9), respectively, are formed. The oxime (13) and the phenylhydrazone (14), under similar conditions, give the methyl piperidin-2-ylideneacetates (16) and (17). The mechanisms of the ring-opening reactions are discussed. Compound (7) is converted spontaneously into N-(trans-3-methoxyacryloyl)-2-pyrrolidone (12), which has been synthesised.