Oxidants lead tetraacetate

Maleic diamide has been cyclized by strong oxidants, lead tetraacetate, or phenyliododiacetate to substituted uracils in high yield (27RTC268 90AJC451) Scheme 14). 

The Diels-Alder ene (213) is also prepared in situ by mild oxidation (lead tetraacetate or f-butyl hypochlorite). It forms many adducts, two of which are shown in Scheme 65. 

Pyridazines were also formed from dioximes by oxidative cyclization [78H(9)1367 79JOC3524 82M118]. As oxidants, lead tetraacetate or phe-nyliodoso bis(trifluoroacetate) were used, and substituted pyridazine 1,2-dioxides 55 are obtained accompanied by isoxazoles, isoxazoloisoxazoles, and open chain compounds. It was also established that a compound to which the structure of 3,6-diphenylpyridazine 1,2-dioxide was previously assigned is, in fact, a dihydroisoxazoloisoxazole derivative (79JOC3524). 

Two oxidants essentially dominate these oxidations lead tetraacetate in organic solvents and periodic acid in aqueous media. On occasion, other oxidation reagents cause the cleavage of vicinal diols ceric ammonium nitrate [424], sodium bismuthate [482, 483], chromium trioxide [482, 555], potassium dichromate with perchloric acid [949], manganese dioxide [817], and trivalent [779, 789] or pentavalent [798] iodine compounds. 

Miscellaneous oxidations. Lead tetraacetate in acetic acid at 35° oxidizes 1-benzenesulfonamidonaphthalene (1) to N-benzenesulfonyl-l,4-naphthoquinone-4-imine (2) and it oxidizes 2-benezenesulfonanudonaphthalene (3) to 2-benzene-sulfonamido-1,4-naphthoquinone (4). ... 

Although, in general, the two oxidants lead tetraacetate and periodic acid give the same results144 and the former has usually been preferred because it is cheaper, it should be noted that periodic acid has the virtue of being more selective. For instance, lead tetraacetate but not periodic acid attacks ditertiary glycols and a-hydroxy acids thus only lead tetraacetate, as shown by Oeda,145 converts 2-hydroxy-3-phenylpropionic acid into phenylacetaldehyde ... 

The pyrrole 23 was also oxidized to 26 using nitric acid, chromium(VI) oxide, lead tetraacetate in acetic acid, or phosphorus pentachloride in phosphorus oxychloride followed by hydrolysis in yields of up to 63%. However, hydrogen peroxide in acetic acid gave a mixture of the epoxy ketone 29 and the amide 30 29 was converted to 30 with ammonia, possibly via rearrangement of an intermediate (31)42 Oxidation of the N-methyl derivative of 23 gave pyrrolenineonium salts, which were difficult to purify.42... 

When an arylthallium compound is treated with the oxidant lead tetraacetate [Pb (OAC) i ] together with triphenyl-phosphine [P(Ph)3], it is oxidized to an aryl trifluoro-acetate. This, when hydrolyzed, yields the phenol after subsequent acidification. To obtain p-cresol by thallation, we would use the following sequence. 

In the pilot-plant procedure, the oxidant lead tetraacetate was replaced, for the environmental benign, by sodium periodate, and the salt 385 was obtained after washings with acetone in 48-57% overall yield and >99.7% ee. The imine Reformatsky reaction was performed on a scale that started from 240 kg of the aldehyde 380. After the batch of the adduct 383 had been spht in two, the subsequent steps led to a combined amount of 350 kg of crystalline ester 385. The sequence shown in Scheme 4.83 is suitable to demonstrate that enolate chemistry, when carefully optimized, is applicable in over 100-kg scale. 

The benzyl group has been widely used for the protection of hydroxyl functions in carbohydrate and nucleotide chemistry (C.M. McCloskey, 1957 C.B. Reese, 1965 B.E. Griffin, 1966). A common benzylation procedure involves heating with neat benzyl chloride and strong bases. A milder procedure is the reaction in DMF solution at room temperatiue with the aid of silver oxide (E. Reinefeld, 1971). Benzyl ethers are not affected by hydroxides and are stable towards oxidants (e.g. periodate, lead tetraacetate), LiAIH, amd weak acids. They are, however, readily cleaved in neutral solution at room temperature by palladium-catalyzed bydrogenolysis (S. Tejima, 1963) or by sodium in liquid ammonia or alcohols (E.J. Rcist, 1964). 

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). 

The most suitable oxidizing agent is potassium ferricyanide, but ferric chloride, hydrogen peroxide ia the presence of ferrous salts, ammonium persulfate, lead dioxide, lead tetraacetate or chromate, or silver and cupric salts may be useful. Water mixed, eg, with methanol, dimethylformamide, or glycol ethers, is employed as reaction medium. 

Cleavage of an alkenoic acid can be carried out with permanganate, a permanganate—periodate mixture, periodate or with nitric acid, dichromate, ozone, or, if the unsaturation is first converted to a dihydroxy compound, lead tetraacetate (71,73). Oxidative ozonolysis is a process for the manufacture of azelaic acid [123-99-9] and pelargonic acid (74). 

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. 

From the preceding examples it can be seen that oxidants and electrophilic reagents attack pyrroles and furans at positions 2 and 5 in the case of indoles the common point of attack is position 3. Thus autoxidation of indoles e.g. 99) gives 3-hydroperoxy-3H-indoles (e.g. 100). Lead tetraacetate similarly reacts at the 3-position to give a 3-acetoxy-3H-indole. Ozone and other oxidants have been used to cleave the 2,3-bond in indoles (Scheme 30) (81BCJ2369). 

Lead tetraacetate is often used as the oxidizing agent for the conversion of hydrazones into ring-fused systems. 

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. 

If the pyrazolone is unsubstituted on position 1, there is still another possibility lead tetraacetate oxidation of (397) yields the oxopyrazolenine (398) (73CRV93) which is a very reactive azadienophile (73JCS(P1)221). 

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

Benzisoxazole N-oxides have recently been synthesized from 2-hydroxypropio-phenone oxime and lead tetraacetate (equation 63) (80CC421). 

Other approaches to the generation of the azallyl cation have been found. One of the most useful involves the use of lead tetraacetate (73TL2143). The anodic oxidation of aziridines also leads to the azallyl cation intermediate (75JA1600). 

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]. 

Dissolved in hot glacial acetic acid, any lead oxide being removed by filtration. White crystals of lead tetraacetate separated on cooling. Stored in a vacuum desiccator over P2O5 and KOH for 24h before use. 

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