Synthesis of 2-Isoxazoline <i>N</i>-Oxides by Copper-Mediated Radical Annulation of Alkenes with α-Nitrobenzyl Bromides

Abstract

Copper-mediated [3 + 2] annulation of alkenes with α-nitrobenzyl bromides has been developed. The reaction is promoted simply by a copper salt to produce the corresponding 2-isoxazoline <i>N</i>-oxides with perfect regioselectivity. The present method can be conducted under mild conditions, affording a diverse array of 2-isoxazoline <i>N</i>-oxides. The obtained products can readily be converted to the related heterocycles such as 2-isoxazoline and isoxazole. A radical-polar crossover pathway initiated by single-electron transfer from nitronate to a copper salt is proposed.