THE CHEMISTRY OF TETRAKIS(TRIFLUOROMETHYL)CYCLOPENTADIENONE

Studies aimed at understanding the reactivity of tetrakis(trifluoromethyl)cyclopentadienone (TTFC, 1) are reported. Reactions between 1 and phosphines were found to afford the kinetic adducts 3 which arise from regiospecific nucleophilic addition of PR3 to the carbon adjacent to the carbonyl group of TTFC. Thermolysis of solutions containing 3 resulted in facile C to O rearrangement of PR3 and yielded the thermodynamic ylides 2. Irradiation of the thermodynamic ylides 2 led to photoreversion back to the kinetic adducts 3. Mechanistic studies indicate that these rearrangements proceed through a dissociative pathway involving P-C (thermal) or P-O (photochemical) bond heterolysis. Fluoride reacted with TTFC in a similar regiospecific fashion to give the adduct 5. By using magnetization transfer techniques, we have discovered a rare example of what is formally a reversible 1,3-fluorine migration in 5. Nucleophiles containing protons attached to the heteroatoms (HX) yielded products (6) derived from formal addition of HX across one of the C = C double bonds of 1. One-electron reduction of TTFC provided the stable radical anion salt 12, while electrochemical studies showed a reversible one-electron reduction wave at E1/2 = +0.37 V (vs SCE) for 1. Chemical reduction of TTFC with trialkylsilanes afforded siloxydienes which could be deprotonated to give the corresponding trifluoromethyl-substituted cyclopentadienide salts (16-18) in good yields. The possible intervention of a single-electron-transfer mechanism in nucleophilic addition reactions involving 1 is discussed.