Lead tetrabenzoate

The close similarity in the isomer ratios obtained from different sources of the phenyl radical suggests that the mechanism of aryla-tion is independent of the nature of the reagent which generates the radical. This principle has been used in reverse in that the constancy of isomer ratios has been cited as evidence that the decomposition of lead tetrabenzoate gives free phenyl radicals. 

Oxidation with mercuric acetate, lead tetrabenzoate, lead dioxide in the presence of 2.4.6-triphenylphenol or other oxidizing agents usually does not give the radical cation of 2.4.6-triphenyl-X -phosphorins, but rather the radical cation of... 

Lead(IV) salts will a-oxygenate enol ethers as they do enols vide supra), although in this case the process involves bisoxygenation of the unsaturated Ullage and subsequent hydrolysis. For example, the combination of lead tetrabenzoate and triethylammonium fluoride at 0-25 C effects efficient a-benzoyl-oxylation, e.g. (68) to (69). 0, y-Unsaturated ketones are also successfully oxidized, e.g. (70) to (71). The correspon ng LTA a-acetoxylations are possible, but the benzoate salt remains the transition metal reagent of choice for these substrates.These reactions appear to be uniformly efficient and perluq)S deserve wider synthetic tq>plication. 

Other reagents have been utilized for this transformation. For example, lead tetrabenzoate (with fluoride-induced hydrolysis of (136) and (137). However, success is restricted to acyclic ketones. Where cyclic dienol ethers are employed, products derived from a-oxidation are obtained. ... 

Lead oxide (yellow), 536-537 Lead tetraacetate, M8, 537-563, 534, 535, 731,1150,1151 Lead tetrabenzoate, 563 Lead tetrafluorlde, 563-464 Lead thiocyanate, 1132,1133... 

Lead tetrabenzoate, Pb(OCOC6Hs)4. Mol. wt. 691.65. Preparation. The reagent is an oxidant similar to lead tetraacetate. ... 

Regiospecific preparation of a-benzoyloxy carbonyl compounds by lead tetrabenzoate (LTB) oxidation of the trimethylsilyl enol ethers is possible. Similarly, a-thiolated ketones can be prepared from a disulfide. 71... 

Phenyl radicals can be generated by the thermal decomposition of lead tetrabenzoate,27 phenyl iodosobenzoate,28 and diphenyliodonium hydroxide,29 and by the electrolysis of benzoic acid.30 These methods have been employed in the arylation of aromatic compounds, including heterocycles. A method of promise which has not been applied to the arylation of heterocycles is the formation of aryl radicals by the photolysis of aromatic iodides at 2537 A.31... 

Reaction of enol silyl ethers with lead tetrabenzoate followed by treatment with triethylammonium fluoride leads to the a-benzoyloxyketones. In both cases, the sequence involves bisoxygenation of the double bond followed by hydrolysis. a-Acetoxylation is also possible, but the benzoate is the reagent of choice for that system. i In the cyclohexanone series, reaction of lead tetraacetate with cyclohexanone trimethylsilyl enol ether afforded also a-acetoxycyclohexanone after hydrolysis." When the same reaction was performed on the triethyltin enol ether, the main product was now a-acetoxycyclohexanone with a small amount of dimeric product. This latter result could be explained by a transmetallation followed by ligand coupling, in the major pathway. 

Lead tetraacetate-N-Bromosuccinimide [1, 563, before Lead tetrabenzoate]. 

Oxidation of trimetkylsilyl enol ethers. The reaction of these enol ethers with lead tetrabenzoate in methylene chloride (20°) followed by treatment with triethylammonium fluoride affords a-benzoyloxy carbonyl compounds in high yield (equation I),... 

A high-yield regiospecific method for the preparation of a-benzyloxy carbonyl compounds has been reported. This entails reaction of the trimethylsilyl enol ether with lead tetrabenzoate many of the difficulties encountered when lead tetraacetate is employed in a similar role are circumvented. ... 

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