REACTION OF BETA-KETO ETHYLENEACETALS WITH HYDROXYLAMINE

A reaction of 2-(2-nitrobenzoylmethyl)-1,3-dioxolane (3) with hydroxyl amine, followed by acid catalyzed cyclization, produced 5-(2-nitrophen yl)isoxazole (5) as the only isolable product, whereas 2-(benzoylmethy l)-1,3-dioxolane ( 9) under identical conditions produced a 2.5:1 mixt ure of 3-phenyl and 5-phenylisoxazoles 10 and 11. These findings contr adict the literature report that beta-keto ethyleneacetals on treatmen t with hydroxylamine produce exclusively 3-substituted isoxazoles. As an additional proof, 3-(2-nitrophenyl)isoxazole (8) was prepared by an unambiguous method via the nitrile oxide route for comparison. The in termediate obtained on treatment of 2-(2-nitrobenzoylmethyl)-1,3-dioxo lane (3) with hydroxylamine was found to be an isomeric mixture of 5-h ydroxy-5-(2-nitrophenyl)-2-isoxazoline (4) and the syn and anti mono-o ximes 19 (at least in solution), either of which could give 5-(2-nitro phenyl)isoxazole (5) on acid treatment. A mechanistic rationale is pro vided to explain the anomalous results.