With Lead Tetraacetate

Diaryl tellurium compounds are cleanly oxidized at 20° to diaryl tellurium diacetates by lead tetraacetate in benzene or toluene. The isolation of the diaryl tellurium diacetates, which are soluble in aromatic hydrocarbons, is facilitated by the precipitation of lead diacetate . 

Diphenyl Tellurium Diacetate A solution of 5.04 g (18 mmol) of diphenyl tellurium in 25 ml of benzene is added over 25 min to a well-stirred solution of 7.92 g (18 mmol) lead tetraacetate in 50 ml of benzene at 20°. The mixture is stirred for 4 h, the white precipitate is filtered off, and the benzene is evaporated from the filtrate. The residue is recrystallized from benzene/hexane (1/9, v/v) yield 7.0 g (98%) m.p. 141°. 

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An unactivated methyl group can be functionalized by the cyclopalladation of oximes. The equatorial methyl of geminal methyls in steroids or hexapyr-anosides is selectively aceto.xylated by the reaction of the palladation complex 523 of the 3-oxime with lead tetraacetate[467,468]. 

R = cyl), eg, with -nitrobenzoyl chloride. Upon reaction with lead tetraacetate, di(hydroperoxyalkyl) peroxides can also be converted to cycHc diperoxides (4). They are also converted to symmetrical or unsymmetrical cycHc triperoxides (5) in the presence of a second ketone and a catalyst, eg, CuSO -HCl (44,119). 

Treatment of (89) with lead tetraacetate generates the unstable open-ring aldehyde (90) which is quickly converted to a dimethylacetal (91). Following basic hydrolysis of the methyl ester and acetates, the acetal is cleaved with aqueous acid to produce TxB2. A number of other approaches, including one starting from the Corey aldehyde, have been described (58). 

The moderate resistance of DMSO to oxidation permits it to be used as a solvent for oxidations with lead tetraacetate or the 2-nitropropane anion (33,34). Dichromate oxidation and permanganate oxidation have been used for quantitative deterrnination of DMSO (35,36). 

Pyridazine-3,6-diones (diazaquinones) are prepared from cyclic hydrazides by oxidation with lead tetraacetate or other oxidizing agents, such as r-butyl hypochlorite, chlorine or nickel peroxide. 

Scheme 59). If phenyliodoso bistrifluoroacetate is used as the oxidizing agent the major product is an isoxazoloisoxazole, but pyridazine 1,2-dioxides are formed in minor amounts together with other products. With lead tetraacetate, in general, pyridazine 1,2-dioxides are the major products. 

In a similar manner to the formation of pyridazines from AT-aminopyrroles, cinnolines or phthalazines are obtainable from the corresponding 1-aminooxindoles or 2-amino-phthalimides. If the relatively inaccessible 1-aminooxindoles are treated with lead tetraacetate, mercuric acetate, r-butyl hypochlorite (69JCS(C)772) or other agents, cinnolones are formed as shown in Scheme 105. The reaction was postulated to proceed via an intermediate... 

Ring-fused systems have also been prepared using this bond formation approach. Treat-ent of the /3-aminoketone (281) with lead tetraacetate gave the isoxazole system (282 ... 

Although some of the oxidative ring closures described above, e.g. reactions with lead tetraacetate (Section 4.03.4.1.2), may actually involve radical intermediates, little use has been made of this reaction type in the synthesis of five-membered rings with two or more heteroatoms. Radical intermediates involved in photochemical transformations are described in Section 4.03.9. Free radical substitutions are described in the various monograph chapters. 

CPB2267) and the oxidation of (277) with lead tetraacetate results in ring expansion to give the 1,2,3-triazine (532) (79YZ699). 

The procedure described here serves to illustrate a new, general method for effecting the < -arylation of g-dicarbonyl compounds by means of an aryllead triacetate under very mild conditions. Although the first synthesis of an aryllead triacetate was reported relatively recently, a wide range of these compounds can now be readily prepared. The most direct route to these compounds is plumbation of an aromatic compound with lead tetraacetate, and in the procedure reported here p-methoxyphenyllead triacetate has been prepared in this way. It may also be obtained by reaction of the diarylmercury with lead tetraacetate, a longer, but more general method of synthesis of aryllead triacetates. 

Dibenz[yellow-green colour (due to other pentacyclic impurities) has been removed by crystn from benzene or by selective oxidation with lead tetraacetate in acetic acid [Moriconi et al. J Am Chem Soc 82 3441 7960]. 

One-electron oxidation of carboxylate ions generates acyloxy radicals, which undergo decarboxylation. Such electron-transfer reactions can be effected by strong one-electron oxidants, such as Mn(HI), Ag(II), Ce(IV), and Pb(IV) These metal ions are also capable of oxidizing the radical intermediate, so the products are those expected from carbocations. The oxidative decarboxylation by Pb(IV) in the presence of halide salts leads to alkyl halides. For example, oxidation of pentanoic acid with lead tetraacetate in the presence of lithium chloride gives 1-chlorobutane in 71% yield ... 

Reaction of Olefins with Lead Tetraacetate and Hydrogen Fluoride... 

Oxidation with lead tetraacetate, 243 preparation of 3/3-hydroxy-18-methyl-androst-4-en-17-one from 18-methyl-pregn-4-ene-3/3,17o ,20-triol, 243... 

Rao prepared 2a-methyl-5a-cholestan-2i -ol (5) by reaction of methyl-magnesium iodide with 5a-cholestan-2-one (4). The 2i -configuration of the hydroxyl group was established by converting (5) to the 2a-methyl-2j5,19-epoxide (6) with lead tetraacetate and iodine in boiling benzene. 

A direct method for introduction of a C-21 acetoxyl group into a 20-keto-pregnane is by reaction with lead tetraacetate at room temperature. Although originally the reaction carried out in hot acetic acid gave low yields, a careful study by Henbest has defined conditions so that yields as high as 86 % can be obtained at room temperature. The preferred solvent is 5 % methanol in benzene, with boron trifluoride etherate as catalyst. With either methanol or benzene, the yield is less than 4%. 

The radical X is formed by homolysis of the X—R bond either thermally or photolytically. In the reactions of alcohols with lead tetraacetate evidence suggests that the X—R bond (X = 0, R = Pb(OAc)3) has ionic character. In this case the oxy radical is formed by a one electron transfer (thermally or photochemically induced) from oxygen to lead. 

The oxidation of alcohols with lead tetraacetate was the first reaction used for oxygenation of an angular methyl group in steroids. It is a simple and efficient method and produces tetrahydrofuran derivatives directly from alcohols. 

However, treatment of the 20-cyanohydrins with lead tetraacetate in the absence of iodine regenerates the 20-ketones and HCN. 

The lla-hydroxy-11,19-cyclo steroids are very efficiently converted into 19-acetoxy-11-ketones by treatment with lead tetraacetate in benzene. ... 

Diosphenol (58) is easily prepared in 47 % yield from testosterone (60) by acetoxylation with lead tetraacetate followed by oxygenation in an alkaline medium. 

Great differences m product structures and distnbuaons are obtained dunng oxidation with lead dioxide or tetraacetate in different solvents and media [63, 64,65J Oxidation of pentafluorophenol with lead tetraacetate gives perfluoro-2,5-cyclohexadien-l-one in good yield [6 ] (equation 57)... 

Destruction of the aromatic ring is the mam reaction in the oxidation of tetrafluoro-o phenyleiiediamine with lead tetraacetate by products are tetrafluorobenzotnazole and tetrafluorochinoxalme denvatives [92] (equation 85) Polyfluonnated benzylideneanilines are oxidized by peroxyacids to different products dependmg on reaction contitions at room temperature the benzylidene carbon is oxidized with the formation of peroxy bonds [93 94] (equation 86), whereas in refluxing agent, the azomethme bond is cleaved [93] (equation 86) Pentafluorobenzylidencanilme is oxidized by peroxyacetic acid in dichlo-romethane at room temperature to perfluorobenzoic acid in a 77% yield [93]... 

Since 1,5-enediones are usually obtained via pyrylium salts, syntheses of the type found in Section B, 2, a have a rather theroetical interest, save for a few special syntheses. There exist several direct syntheses of l,5-enediones, e.g., from j8-chlorovinyl ketones and j8-diketones or j8-keto esters special pathways to 1,5-enediones have also been described, namely, oxidation with lead tetraacetate or with periodic acid of cyclopentene-l,2-diols. ... 

The methyl ester of 2-phenyloxazole-4-carboxylate gives the 5-methyl-derivative when methylated with lead tetraacetate. ... 

The oxidative cleavage of the central carbon-carbon bond in a vicinal diol 1, by reaction with lead tetraacetate or periodic acid, yields two carbonyl compounds 2 and 3 as products. 

Conjugate addition of methyl magnesium iodide in the presence of cuprous chloride to the enone (91) leads to the la-methyl product mesterolone (92) Although this is the thermodynamically unfavored axially disposed product, no possibility for isomerization exists in this case, since the ketone is once removed from this center. In an interesting synthesis of an oxa steroid, the enone (91) is first oxidized with lead tetraacetate the carbon at the 2 position is lost, affording the acid aldehyde. Reduction of this intermediate, also shown in the lactol form, with sodium borohydride affords the steroid lactone oxandrolone... 

Nabilone (37) is a synthetic 9-ketocannabinoid with antiemetic properties. One of the best of the various published routes to nabilone starts with the enolacetate of nopinone (33), which on short heating with lead tetraacetate undergoes allylic substitution to give Treatment with p-toluene-... 

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