Lead tetraacetate quinones

This reaction is most often carried out with R = aryl, so the net result is the same as in 14-17, though the reagent is different. It is used less often than 14-17, but the scope is similar. When R = alkyl, the scope is more limited. Only certain aromatic compounds, particularly benzene rings with two or more nitro groups, and fused ring systems, can be alkylated by this procedure. 1,4-Quinones can be alkylated with diacyl peroxides or with lead tetraacetate (methylation occurs with this reagent). 

The decarboxylation of carboxylate anions is carried out chemically by a variety of one-electron oxidants such as lead tetraacetate, uranyl nitrate, peroxides, quinones, pyridinium cations, etc.199 Importantly, the carboxylate anion (as... 

Lead tetraacetate is a versatile reagent which has many applications in organic synthesis, not least in the synthesis of quinones. ... 

Lead tetraacetate was employed by Stoodley and coworkers for an oxidative isomerization in their synthesis of 4-demethoxydaunomycinone (47). The diene (48) reacted with the oxirane dienophile (49) via the least hindered endo transition state to give the cycloadduct (50) in 86% yield. Hydrolysis of the silyl enol ether followed by reduction of the oxirane and introduction of the acetylene moiety gave the compound (51), which was oxidatively isomerized with LTA in acetic acid to give the quinone (52). All that remained now to complete the synthesis was conversion of the acetylene to a methyl ketone and dealkylation of the ether, llie last two steps were accomplished in an over l yield of 38%, the low yield attributable to problems in formation of the hydroxy group from the ether (Scheme 11). Bulman-Page and Ley employed LTA for a similar transformation in their synthesis of demethoxydaunomycinone and related anthracyclinones. 

Oxidation of 2,5-diethoxy-3,6-dihydropyrazine with dichlorodicyanobenzo-quinone (DDQ) formed 2,5-diethoxypyrazine (314), and the 3,6-dimethyl analogue reacted similarly (314). 2,5-Diisopropyl-3,6-dimethyl-2,5-dihydropyrazine was oxidized in alkaUne solution to 2,5-diisopropyl-3,6-dimethylpyrazine (225). Oxidation of 2,5-diethoxy-3,6-dimethyl-3,6-dihydropyrazine with lead tetraacetate in refluxing benzene gave both 2,5-diethoxy-3,6-dimethylpyrazine (minor product) and 2,5-diacetoxy-3,6-diethoxy-2,5-dimethyl-2,5-dihydropyrazine (1068). 

The isomeric pyridopyridazinediones were oxidized with lead tetraacetate to give the unstable quinones 234 and 235, which were trapped with cyclo-pentadiene (73JCS(P1)26). 

Aryl coupling to a benzylic site has also been observed the monophenol (67) yielded the aryltetralin (68 55%), with thallium trifluoroacetate-boron trifluoride. Probably oxidation to quinone methide precedes the ring closure. Separate oxidation and cyclization steps were employed in the synthesis of ( )-thaliphotphine acetate. ( )-Codamine (69) underwent Wessely oxidation with lead tetraacetate to the acetoxycyclohexadienone (70), which closed in acetic anhydride-acid to ( )-thaliphorphine acetate (71), albeit in modest overall yield (14%). ... 

Me thylation. Discovery of this reaction was the result of a chance observation made by one of us in attempting to improve a known procedure for converting butadiene-toluquinone (I) into 2-methyl-1,4-naphthoquinone (IV). Oxidation of the isomerized product II with silver oxide stops at the stt e of the highly sensitive quinone III. Chromic acid carried the oxidation to the desired stage but affords IV in yield of only 50%. Lead tetraacetate might either acetoxylate one of the activated... 

Methylation or Quinones, nitroaromatic cxjmpounds Lead tetraacetate. 

The construction of only the (S)-hexahydroxydiphenyl unit, a structural analog of secondary plant metabolite ellagitannins, by biomimetic cyclization of suitably protected glucose-derived digaUoyl esters has been achieved by use of lead tetraacetate (Scheme 13.32). No quinone ketal-type product was detected, in contrast to the simpler system described below (Scheme 13.37). 

In acetic acid lead tetraacetate usually oxidizes phenols to the corresponding quinones or their derivatives. The product is highly dependent on the substituents on the aromatic ring. The reaction of dimethoxyphenol with lead tetraacetate furnished the monooxidation product quinone ketal in excellent yield (Scheme 13.37 compare with Scheme 13.32) [55]. 

Benzynequinone. Oxidation of the quinone (1) in methylene chloride with lead tetraacetate in the presence of tetracyclone leads to 6,7,8,9-tetraphenyl-l,4-naphthoquinone (2) in about 40% yield. Benzynequinone is evidently formed and is trapped by tetracyclone with decarbonylation of the original adduct. ... 

Dehydrogenation of pyrocatechol by silver oxide gives 0-benzoquinone.469 For preparation of amino-0-benzoquinones see Homer and Lang.470 Hydro-quinones are also dehydrogenated with success by lead tetraacetate.222 Further, 2,3-dichloro-5,6-dicyano-l,2-benzoquinone is obtained from the hydroquinone in 83% yield when a solution of the latter in 5% ethanolic hydrogen chloride is shaken with a mixture of Pb02 and benzene.471... 

Note that catechols (1,2-dihyroxybenzenes) are readily oxidized to o-quinones, l5 but the products are often sensitive to the electrophilic or nucleophilic species in the reaction medium. Catechol itself gives 125. Dimerization is as much a problem with catechols as with monophenols (see Table 3.4). The conversion of catechol to 125 used silver carbonate and it is noted that silver salts are the classical oxidation reagent for such transformations. Other reagent have been used to oxidize catechol derivatives, including ceric sulfate, lead tetraacetate, DDQ (2,3-dichloro-5,6-dicyano-l,4-benzoquinone), iodate, and periodate. ... 

Oxidative cyclization of quinone-derived enaminones with lead tetraacetate gives access to the isoxazoloquinones. Thus, oxidation of the enaminones 291 and 292 gives the isoxazoloquinones 293 and the naphth[2,3-c]isoxazoloquinone 294, respectively. Scheme 80 (74S30 85JHC697). 

Oxidation of o-qtSnones. c ,cis-Muconic acid dimethyl esters are obtained (60-907o yield) by oxidation of o-quinones with lead tetraacetate in CeH -CH30H(1 1). ... 

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