Novel condensations of nitroacetic esters with aromatic aldehydes leading to 5-hydroxy-1,2-oxazin-6-ones

Contrary to the early literature [Dornow, A.; Wiehler, G. Justus Liebigs Ann. Chem. 1952, 578, 113–121], esters of 2,4-dinitro-3-arylglutaric acids 2 could not be obtained by double condensation of aryl aldehydes with alkyl nitroacetates. Instead, under these conditions, we observed formation of novel 4-aryl-5-hydroxy-1,2-oxazin-6-one-3-carboxylates 1. The roles of the solvent, the reaction conditions, and the nature of the reagents in this new condensation were investigated. The data obtained suggest that the heterocyclic products 1 originate from intramolecular oxidation (similar to the Nef reaction) of dinitro derivative 2, followed by nucleophilic attack of the oxime oxygen at the carboxylate group. The condensation presented provides a novel general synthetic route to these types of heterocycle.