Synthesis of 9-substituted xanthenes by the condensation of arynes with ortho-hydroxychalcones

The reaction of o-(trimethylsilyl)aryl triflates, CsF, and o-hydroxychalcones affords a general and efficient way to prepare biologically interesting 9-substituted xanthenes. This chemistry presumably proceeds by the tandem intermolecular nucleophilic attack of the phenoxide of the chalcone on the aryne and subsequent intramolecular Michael addition. The introduction of an external base, Cs2CO3, has proven beneficial in this reaction.