Structural characterization of strained oxacycles by 13C NMR spectroscopy

Abstract

The 1 H and 13 C NMR data of a series of epoxy-and epidioxy-bridged tetrahydropyran derivatives containing the same basic carbon skeleton, are reported. 13 C NMR spectroscopy was shown to be useful for structural determination of both substructures allowing facile distinction of otherwise similar compounds.

Studies on Biomimetic Singlet Oxygen Oxidations: Application to the Synthesis of the Alkaloid Simulenoline

“…The structure of these products arising from sequential [4 + 2] and ene-type photooxygenation events with 1 O 2 was established by 1D and 2D NMR analysis as well as comparison with data of known related 1,2,4-trioxanes. 30 Unlike precursor 4d, which previously exhibited almost exclusive reaction at the pyran system, 9 in our series of 2-prenyl-2H-pyrans, the lack of extra conjugation of the oxacycle (as in 19) seems to be essential for it to compete as a diene with the pendant olefin for 1 O 2 .…”

“…The remaining substrate evaluated, 2 H -pyran 19 , also led to a complex photooxygenation crude mixture after complete conversion in 1 h. One fraction of this crude mixture, representing a yield of 50%, consisted of an inseparable mixture of trioxanic alcohols 20 and 21 . The structure of these products arising from sequential [4 + 2] and ene-type photooxygenation events with 1 O 2 was established by 1D and 2D NMR analysis as well as comparison with data of known related 1,2,4-trioxanes …”