Lead(IV) Trifluoroacetate1


[16656-82-9]  · C8F12O8Pb  · Lead(IV) Trifluoroacetate  · (MW 659.13)

(functionalization of saturated hydrocarbons;2 trifluoroacetoxylation, plumbation, and dimerization of substituted benzene derivatives;3,4 oxidation of alkenic compounds5)

Alternate Name: lead tetrakis(trifluoroacetate); LTTFA.

Physical Data: too hygroscopic for mp determination.

Solubility: reacts with aliphatic and aromatic hydrocarbons (such as heptane, benzene, toluene, etc.), but is stable and sol in trifluoroacetic acid (TFA), C6F6, CH2Cl2, and MeNO2.

Form Supplied in: commercially available in the form of white crystals moistened with TFA. Drying: for some reactions, TFA must be completely removed; this is achieved by drying the reagent in vacuo (over KOH and P2O5) for several days.

Analysis of Reagent Purity: the oxidizing capability and purity of the reagent can be determined iodometrically.

Preparative Method: can be prepared in situ from Lead(IV) Acetate and Trifluoroacetic Acid.

Handling, Storage, and Precautions: the solid reagent is very reactive and hygroscopic, and must be stored in the dark, in the absence of moisture, and below 10 °C.

Functionalization of Saturated Hydrocarbons.

The powerful oxidizing properties of lead tetrakis(trifluoroacetate) have been used for the introduction of functional groups on nonactivated carbon atoms,1a particularly of bridged hydrocarbons.2,6 In these reactions, generally performed at rt, LTTFA is generated in situ from lead tetraacetate (LTA) and an excess of TFA in CH2Cl2 as solvent (eq 1).2,6 The reactivity of the labile trifluoroacetoxy ester group permits alternative functionality to be introduced.7 Thus by running the LTTFA oxidation of adamantane in the presence of acetonitrile, N-(1-adamantyl)acetamide is obtained in 85% yield.6,7 Other nucleophiles such as CN-, RS-, Ar-, and C- can also be introduced on bridged carbon atoms in this way.7 Only monosubstituted derivatives are obtained.2

Trifluoroacetoxylation of Benzenoid Compounds.

The synthesis of p-substituted aryl trifluoroacetates can be conveniently achieved in yields up to 76% by reaction of substituted benzenes with LTTFA in TFA (eq 2).4,8 Nitrobenzene fails to react after two weeks at rt, while anisole reacts very violently.8 Aryllead tris(trifluoroacetates) as intermediates are also formed from the corresponding arylmercury(II) or arylthallium(III) trifluoroacetates and from aryltrimethylsilanes, upon reaction with LTTFA.4,9,10 The aryltrifluoroacetate esters are usually hydrolyzed and isolated as the corresponding phenols.3,4

By oxidation of methyl substituted benzenes with LTTFA (LTA + TFA) in TFA and CH2Cl2 at low temperature (0 °C or below), coupling occurs producing biaryl and diarylmethane compounds (7-65%) (eq 3).11

Oxidation of Alkenic Compounds.

LTTFA, as an electrophilic oxidizing agent, reacts readily with alkenic bonds. Thus styrene and substituted styrenes undergo oxidative rearrangement to give 1,1-bis(trifluoroacetoxy) derivatives, which are easily hydrolyzed to the corresponding carbonyl products (eq 4).12,13

Conjugated dienes also react with LTTFA and undergo 1,4-addition, affording 1,4-bis(trifluoroacetate) esters (eq 5).12

When treated with LTTFA, allylic hydroxy steroids are converted to epoxy trifluoroacetates (eq 6), whereas homoallylic steroid alcohols undergo C-C bond cleavage to give secosteroid compounds.5

Hydroxysulfenylation of alkenes to 1,2-hydroxythio ethers, via the corresponding trifluoroacetoxy addition intermediates, is readily achieved by means of LTTFA (LTA + TFA) and diaryl disulfides in TFA/CH2Cl2, at low temperature (from 0 °C to -40 °C) (eq 7).14

1. (a) Partch, R. E. JACS 1967, 89, 3662. (b) Convery, R. J. U.S. Patent 2 985 673, 1961 (CA 55, 22 916).
2. Jones, S. R.; Mellor, J. M. JCS(P2) 1977, 511.
3. Norman, R. O. C.; Thomas, C. B.; Willson, J. S. JCS(B) 1971, 518.
4. Kalman, J. R.; Pinhey, J. T.; Sternhell, S. TL 1972, 5369.
5. Westphal, D.; Zbiral, E. LA 1975, 2038.
6. Jones, S. R.; Mellor, J. M. JCS(P1) 1976, 2576.
7. Jones, S. R.; Mellor, J. M. S 1976, 32.
8. (a) Campbell, J. R.; Kalman, J. R.; Pinhey, J. T.; Sternhell, S. TL 1972, 1763. (b) Bell, H. C.; Kalman, J. R.; Pinhey, J. T.; Sternhell, S. TL 1974, 853.
9. De Vos, D.; Wolters, J.; Van der Gen, A. RTC 1973, 92, 701.
10. Norman, R. O. C.; Poustie, M. JCS(C) 1969, 196.
11. Norman, R. O. C.; Thomas, C. B.; Willson, J. S. JCS(P1) 1973, 325.
12. Westphal, D.; Zbiral, E. M 1975, 106, 679.
13. Lethbridge, A.; Norman, R. O. C.; Thomas, C. B. JCS(P1) 1973, 35.
14. Trost, B. M.; Ochiai, M.; McDougal, P. G. JACS 1978, 100, 7103.

&ZZbreve;ivorad &CCbreve;eković & Mihailo Lj. Mihailović

University of Belgrade, Yugoslavia

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