Metal-Free Synthesis of Benzisoxazolones Utilizing <i>ortho</i>-Ester and <i>ortho</i>-Cyano-Functionalized Diaryliodonium Salts with Protected Hydroxylamines

Herein, we report the development of metal-free one/two-pot procedures for the synthesis of benzo[<i>c</i>]isoxazol-3(1<i>H</i>)-one (benzisoxazolone) heterocycles by designing diaryliodonium salts featuring <i>ortho</i>-ester or nitrile functional groups. These react smoothly with protected hydroxylamines under mild conditions to produce <i>N</i>-arylhydroxylamine intermediates, which readily cyclize to give benzisoxazolone derivatives under acidic conditions. This metal-free process maintains the weak N-O bond, tolerates a wide range of diaryliodonium salts and protected hydroxylamines with diverse functional/protecting groups, thereby overcoming the challenges associated with previous transformations. The protocol expands the reaction scope and broadens the chemical space of the fused isoxazolone backbones to include unprecedented five-membered heteroaryl-fused isoxazolones in high yields. This method is also applicable to gram-scale synthesis, and the resulting benzisoxazolones can be effectively derivatized at the <i>N</i>-position to afford valuable compounds.