Metal-Free Oxidative Coupling: Xanthone Formation via Direct Annulation of 2-Aryloxybenzaldehyde using Tetrabutylammonium Bromide as a Promoter in Aqueous Medium

A metal‐free intramolecular annulation of 2‐aryloxybenzaldehydes to xanthones is disclosed, which proceeds through the direct oxidative coupling of an aldehyde CH bond and aromatic CH bonds using tetrabutylammonium bromide (TBAB) as a promoter in aqueous medium. This strategy works smoothly in the presence of both electron‐donating and electron‐withdrawing groups, and displays good tolerance towards catalytically reactive substituents, thus promising further functionalizations of xanthone products.