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

Photooxygenation of titled furans followed by redn. gives unsatd. 4-​oxoaldehydes quant. Some derivs. 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 quant. yields. All the procedures are one-​pot and occur stereoselectively. Due to the electron-​poor substituents alternative non-​photochem. oxidative methods fail or give not cleanly reaction mixts.