Polysubstituted isocoumarins such as thunberginol A were synthesized by the reaction of substituted 2-(trimethylsilyl)-phenyl triflate with trifluoromethylated beta-diketones in the presence of CsF. The reaction proceeded via carbon carbon bond insertion of aryne followed by intramolecular cyclization and CF3 anion extrusion. The -C(center dot center dot center dot O)CF3 unit has high potential for not only the nucleophilic moiety but also a useful leaving group of CF3.