A NOVEL SYNTHESIS OF CYCLOPENTA[D]XANTHONES AND CYCLOHEXA[D]XANTHONES FROM THE REACTION BETWEEN CYCLOALKYL ENAMINES AND 2-HYDROXYPHENYLPENTENE-1,3-DIONES, AND THEIR REARRANGEMENT TO CYCLOPENTA[A]XANTHONES AND CYCLOHEXA[A]XANTHONES

Treatment of (E)-5-substituted-1-(2-hydroxyphenyl)pent-4-ene-1,3-diones 1 with alicyclic ketone enamines 2 rapidly gives the cycloalkano[d]xanthones 3, but on longer treatment or on reaction of 3 with base, cycloalkano[a]xanthones 4 are obtained; their structures, including stereochemistry, were determined from spectroscopic data and, in the case of 3aB, from X-ray diffraction analysis.