Fenton chemistry for Achmatowicz rearrangement

Achmatowicz rearrangement (AchR) is a very important transformation for the synthesis of various heterocyclic building blocks and natural products. Here, the discovery of Fenton chemistry for AchR using a bifunctional catalyst (FeBr₂ or CeBr₃), which has environmental friendliness and a broad substrate scope at the same time has been reported. This method addresses the major limitation of conventional chemical (hazardous) and enzymatic (limited scope) methods. Mechanistic studies suggested that reactive brominating species (RBS) is the true catalyst for AchR and that Fenton chemistry [Fe/Ce (cat.) + H₂O₂ → HO^•/HOO^• + H₂O] is responsible for the oxidation of bromide into RBS. Importantly, this in situ RBS generation from M-Br_x-H₂O₂ under neutral conditions addresses the long-lasting problem of many haloperoxidase mimics that require a strong acidic additive/medium for bromide oxidation with H₂O₂, which creates opportunities for many other brominium-mediated organic reactions.