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.
Keywords: 4-oxo acids, 4-oxoaldehydes, base treatment, furan endoperoxides, reduction, singlet oxygen.
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