Electrophilic Derivatization of Trifluoromethyl-Substituted Semisquarate Using Unsaturated Organosilanes and Subsequent Ring Transformations

To extend the synthetic potential of trifluoromethyl-substituted semisquarate (CF3-semisquarate) previously synthesized by us as a pluripotent building block, its electrophilic derivatization was investigated. The electrophilic addition of allylic silanes and silyl enolates to CF3-semisquarate afforded the corresponding 4-hydroxycyclobutenones. Subsequent ring expansion of these products via thermolysis or oxidation using lead tetraacetate afforded trifluoromethylated bicyclo[3.2.0]heptenones or (Z)-γ-alkylidenetetronates.