Ceric Ammonium Sulfate (CAS) Mediated Oxidations of Benzophenones Possessing a Phenolic Substituent for the Synthesis of Xanthones and Related Products

Work
previously published by our group described novel methodology
for the synthesis of xanthones and related products from phenolic
benzophenones in a reaction mediated by ceric ammonium sulfate (CAS).
In this paper we further explore this novel reaction by subjecting
an additional set of phenolic benzophenones to CAS to afford a range
of compounds, including xanthones, 9H-xanthen-2,9­(4aH)-diones, 3H-spiro­[benzo­furan-2,1′-cyclo­hexa­[2,5]­diene]-3,4′-diones,
and biaryl compounds. A comparison of these reactions with the more
commonly used oxidant ceric ammonium nitrate (CAN) was also conducted.
Based on these results, greater insight into the reaction mechanism
has been gained. In addition, the conversion of the synthesized xanthen-2,9­(4aH)-diones to xanthones by treatment with sodium dithionite
is described.