Polysubstituted isocoumarins such as thunberginol A were synthesized by the reaction of substituted 2-(trimethylsilyl)phenyl triflate with trifluoromethylated β-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(···O)CF3 unit has high potential for not only the nucleophilic moiety but also a useful leaving group of CF3.