Photooxygenation of Electron-Poor Trisubstituted Furans: Novel Aspects and Applications

Photooxygenation of titled furans followed by reduction gives unsaturated 4-oxoaldehydes quantitatively. Some derivatives cyclize under slightly acid conditions or by silica gel to unusual 5,6-dioxabicyclo[2.1.1]hexenes and/or 5H-furanones. Under appropriate basic conditions 4-oxocarboxylic acids or their ring-tautomers 5-hydroxyfuranones are chemoselectively obtained in almost quantitative yields. All the procedures are one-pot and occur stereoselectively. Due to the electron-poor substituents alternative non-photochemical oxidative methods fail or give not cleanly reaction mixtures.