Metal‐Free Oxidative Cyclization of Alkynyl Aryl Ethers to Benzofuranones

Readily available phenols can be converted into substituted aryl alkynyl ethers, which react with an N-oxide as an oxidant and catalytic amounts of a Brønsted acid to provide benzofuranones. If non-terminal alkynyl ethers are applied, a 1,2-hydride shift takes place and phenyl acrylates are obtained. Thus activated alkynes can serve as α-oxy carbene precursors even in the absence of a metal catalyst.