Investigation on the reactivity of isoxazol-5-ones towards 1,2-diaza-1,3-dienes: new entry to variously substituted (imidazol-2-yl)acetate and 1,3-oxazin-6-one derivatives

1,2-Diaza-1,3-dienes (DDs) undergo, under neutral conditions, N-nucleophilic attack from a 4-ethoxycarbonylisoxazol-5-one derivative. The first aza-Michael addition is followed by an intramolecular second, affording a fused heterobicyclic system that, upon ring opening and decarboxylation processes, gives rise to novel substituted imidazoles with an acetate functionality in the 2-position. On the contrary, under the same reaction conditions, 3-phenylisoxazol-5-one provides a double Michael addition at two units of DD involving first the C-4 and then the N-2 of the heterocycle. The resulting diadduct spontaneously undergoes ring-opening/ring-closing process that concludes with a ring enlargement of the heterocycle providing the 1,3-oxazin-6-one derivative.