The Intramolecular Diels-Alder Furan Approach in Synthesis : 11-oxatricyclo|6.2.1.0^1,6|undec-9-en-5-one

References

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• Nelson , W. L. and Allen , D. R. 1972 . J. Heterocyclic Chem. , 9 : 561 Substituted 2,3,6,7-tetrahydro-3a,6-epoxyisoindol-1-ones formed upon intramolecular cyclization6d,7,8 were shown to be trans-fused on the base of their 1H-NMR spectra. The observance of only one vicinal coupling constant (J = 8.4 Hz), for the hydrogen atom at δ 1.54 shows it to be the endo-H7 in the oxabicyclo|2.2.1| heptene system (corresponding to a dihedral angle of 90° between H8 and endo-H7); the magnitude of this value (8.4 Hz) is in accord with the exo-structure 3a : the dihedral angle between H6 and endo-H7 is 0°, whereas the endo-product 3b would show an angle of 120° (J ≃ 4 Hz). These assignments are in agreement with the spectral data obtained for endo- and exo-2-substituted-7-oxabicyclo |2.2.1| hept-5-enes, see
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• Heating at reflux in xylene led to a complex mixture (TLC)
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• Melting points and boiling points are uncorrected. IR spectra were recorded on a Perkin-Elmer 337 spectrometer, 1H-NMR spectra on a Varian EM-390 spectrometer (CDCl3, unless otherwise stated) and mass spectra on a AEI MS-50 mass spectrometer. Rf values are quoted for Merck silica gel 60 GF254 TLC plates of thickness 0.25 mm and for the solvent system ethyl acetate-isooctane (3:7). Florisil was purchased from Merck (100–200 mesh ASTM). Products 1, 3a, 4> and 5 gave satisfactory combustion analyses (C ± 0.9 %, H ± 0.9 %)
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• The furan nucleus gave supplementary bands at 1600, 1510, 1150, 930, 890, 800 and 730 cm-1
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