Quadricyclane—thermal cycloaddition to polyfluorinated carbonyl compounds: A simple synthesis of polyfluorinated 3-oxatricyclo[4.2.1.02,5]non-7-enes

Quadricyclane (1) readily undergoes [2+2+2] cycloaddition reactions with electron-deficient fluorinated carbonyl compounds to give polyfluorinated 3-oxatricyclo[4.2.1.02,5]non-7-enes in high yields. Hexfluoroacetone, trifluoroacetyl chloride, methyl trifluoropyruvate, α-(fluorosulfonyl)difluoroacetyl fluoride, and bis(trifluoromethyl)ketene all react rapidly with 1. Trifluoracetyl fluoride although less reactive, slowly interacts with 1 at ambient temperature. 1,1,1-Trifluoroacetone, trifluoroacetophenone, carbonyl fluoride, and CF3C(O)OC6F5 require higher temperatures (60–90 °C) for reaction, and ethyl trifluoroacetate is unreactive at 90 °C. Heating 1 with the ethyl hemiacetal of trifluoroacetaldehyde gives the corresponding cycloadduct of CF3C(O)H in 44% yield. etane product from hexafluoroacetone is remarkably stable to both acids and bases, whereas the oxetanes with α-F or Cl leaving groups are sensitive to acid-catalyzed rearrangement.