A novel synthesis of cyclopenta- and cyclohexa-[d]xanthones from the reaction between cycloalkyl enamines and 2-hydroxyphenylpentene-1,3-diones, and their rearrangement to cyclopenta- and cyclohexa-[a]xanthones
Abstract
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 spectrosopic data and, in the case of 3aB, from X-ray diffraction analysis.