The Synthesis of Various Cycloalkana[d]xanthones and Conversion of the Cyclohexa-Analogue to a 7,7a-Dimethylcyclohexa[d]xanthene.

The synthesis of cyclo-penta-, -hexa- and -hepta-[d]xanthones 5 from (E)-(2-hydroxyphenyl)-5-arylpent-4-ene-1,3-diones 4, cycloalkanones and pyrrolidine is described. Reactions to modify 5 in an attempt to synthesize analogues of the five naturally occurring cyclohexa[d]xanthenes (with general formula 1) are also described: these reactions include C-methylations at C-7 and C-7a, hydride reduction of the 8-keto group, dehydroxylations and finally catalytic reduction to give 16. The stereochemistry of 16 established by NOE and an X-ray crystal structure of 9aB differs from 1 at two contiguous C-atoms.