Iron‐Promoted Reductive Ring‐Opening and Isomerization Reactions of C4‐Alkynylisoxazoles Leading to 2‐Alkynylenaminones and Polysubstituted Furans

Abstract

AbstractA new iron(III)‐promoted reductive ring‐opening and isomerization reactions of C4‐alkynylisoxazoles in the oxidized N‐methylpyrrolidone (NMP*) was reported. By changing the substituents at the C3 and C5 position of the isoxazole ring, the reaction selectively produced 2‐alkynylenaminones and polysubstituted furans in good to excellent yields. It was very interesting that large group at the C3 or C5 position of the isoxazole ring was a steric hindrance tertiary butyl group (t‐Bu), the reaction proceeded ring‐opening rather than isomerization reaction in the presence of FeCl3. It was noteworthy that the NMP* as a solvent and a hydrogen donor was essential for both reactions. A plausible mechanism for the reductive ring‐opening and isomerization was also proposed.magnified image