Oxidations of Furan Rings in Organic Synthesis: Expanding Synthetic Utility of Aromatic Heterocycles

Controlled oxidation reactions of substituted furans lead to carboxylic acids, butenolides, 1,4-dicarbonyl compounds and pyranones. By virtue of these transformations, the furan ring may be considered as a C-1 or as a C-4 synthon due to its synthetic equivalence to a hydroxycarbonyl anion or a 1,4dicarbonyl unit, respectively. This review surveys the most relevant aspects concerning oxidation reactions of furan systems leading to synthetically useful intermediates.