Alkylation of enamines by α-haloketoximes : Synthesis and properties of some 6-hydroxy-5,6-dihydro-1,2,4 H-oxazines ring-chain tautomerism of γ-oximino carbonyl compounds

Abstract

Alkylation of several enamines by phenacyl or p-bromophenacyl bromide oxime affords the corresponding alkylated immonium salts III. Mild hydrolysis of these salts in most cases yields the unknown 6-hydroxy-4,5-dihydro-1,2,4 H-oxazines (VI). Spectroscopic observation shows that some of these compounds exist in solution only in the cyclic form, some in a ring-chain tautomeric equilibrium with the corresponding γ-oximino carbonyl compounds V. When two dissymmetric centers are present in VI rapid epimerization can be observed at C-6, probably through the open chain form. The chemical behaviour of oxazines VI has been investigated. A Beckmann fragmentation has been observed on one of these oxazines (VIg) when treated with trifluoroacetic acid.