Benzoquinone catalytic hydrogenation

The most common stereoselective syntheses involve the formation and cleavage of cyclopentane and cyclohexane derivatives or their unsaturated analogues. The target molecule (aff-cts)-2-methyl-l,4-cyclohexanediol has all of its substituents on the same side of the ring. Such a compound can be obtained by catalytic hydrogenation of a planar cyclic precursor. Methyl-l,4-benzoquinone is an ideal choice (p-toluquinone M. Nakazaki, 1966). 

Aniline Oxidation. Even though this is quite an old process, it still has limited use to produce hydroquinone on a commercial scale. In the first step, aniline is oxidized by manganese dioxide in aqueous sulfuric acid. The resulting benzoquinone, isolated by vapor stripping, is reduced in a second step by either an aqueous acidic suspension of iron metal or by catalytic hydrogenation. 

Ethoxypenta-l, 3-diene underwent the Diels-Alder reaction withp-benzoquinone to give the cis-fused diketone I. Selective catalytic hydrogenation (Ni) of I, followed by reduction with lithium aluminum... 

With nitrobenzene, reduction to an intermediate stage results in the formation of a complex which, as is also the case with the initial complexes formed with ferricyanide, benzoquinone, and benzaldehyde, cannot react in the manner shown in the first conclusion. These species require the presence of added alkali, which apparently effects the displacement of reduced substrate by hydroxyl anion to yield hydroxypentacyanocobaltate(III). All of the substrates mentioned have been found to undergo catalytic hydrogenation when added to the catalyst system in less than stoichiometric quantities in the presence of alkali. 

An alternate entry to the narciclasine class of alkaloids has provided access to compounds related to isonarciclasine (263) (Scheme 24). In the event, the aryla-tion of p-benzoquinone with diazonium salts derived from the aryl amines 250 and 251 yielded the aryl-substituted benzoquinones 252 and 253, respectively (146). The selective hydroxylation of 252 and 253 with osmium tetraoxide provided the corresponding m-diols 254 and 255. Catalytic hydrogenation of 254 and 255 using Pd/C or Raney Ni and subsequent lactonization gave the triols 256 and 257 together with small amounts of the C-2 a-epimers 258 and 259. Aminolysis of 256 and 257 afforded the corresponding racemic tetrahydrophen-anthridones 260 and 261, whereas similar treatment of the a-epimers 258 and 259 led to the formation of ( )-isolycoricidine (262) and ( )-isonarciclasine (263), respectively. 

Treatment of a 2,5-disubstituted 1,4-dimethoxybenzene 877 with CAN provided a 97% yield of p-benzoquinone 878 °. The fully substituted 1,4-dimethoxybenzene derivative 879 was treated with CAN to afford in 64% yield the quinone monoketal 880. This was submitted to catalytic hydrogenation to give the precursor of a-tocopherol 881 (Scheme 178). A variety of substituted 1,4-dimethoxybenzenes were also oxidized with CAN to give high yields of p-benzoquinones. 

Only activated monoenes are hydrogenated . These include carvene, mesityl oxide, 2-cyclohexenone, and benzalacetone . Some styrenes are hydrogenated a-functionalized styrenes react, but )S-functionalized styrenes do not - " . Similarly, only activated ketones such as benzil, diacetyl and p-benzoquinone are hydrogenated to alcohols " . Often catalytic reduction of a ketone is observed only in the presence of added OH . The base is believed to react with an intermediate to give [Co(CN)j(OH)] and the reduced substrate . Aryl ketones such as acetophenone and benzophenone are not reduced . Several examples of nitro and nitroso compound reductions have been reported - . ... 

The reduction of furoxans by lithium aluminum hydride to give amines,182,283,423,424 and of fused furoxans to diamines283,423 (Section V,D), has potential utility ring cleavages brought about by this reaction show a number of synthetic possibilities. The catalytic hydrogenation of tetrahydrobenzofuroxan to hexamethylenediamine is also potentially useful.279,420 o-Benzoquinone dioxime may be prepared very easily by reduction of benzofuroxan (Section V,D,5). 

On bare platinum the reduction proceeds via catalytic hydrogenation to o-nitroanihne (Scheme 2), which is reduced further to o-phenylenediamine. On the other hand, on UPD-modified platinum surfaces, the reduction occurs at much more positive potentials and follows the electronation mechanism, that is, the direct exchange of electrons between the dinitroso tautomeric form and the modified electrode surface. The first step is now the reduction to o-benzoquinone dioxime that appears as a stable intermediate over a wide potential range (0.60 to 0.45 V) before it is reduced further to the final products. 

Adam, W., Herrmann, W., Lin, J., etal. (1994). Catalytic Oxidation of Phenols to / -Quinones with the Hydrogen Peroxide and Methyltrioxorhenium(VII) System, J. Org. Chem., 59, pp. 8281-8283 Bernini, R., Mincione, E., Barontini, M., et al. (2006). Convenient Oxidation of Alkylated Phenols and Methoxytoluenes to Antifungal 1,4-benzoquinones with Hydrogen Peroxide (H202)/methyltrioxorhenium (CH3Re03) Catalytic System in Neutral Ionic Liquid, Tetrahedron, 62, pp. 1133-1131. 

Oxidation of caUx[4]furans 4 and 7 by nitric acid, cerium(lV) ammonium nitrate, or 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) followed by subsequent treatment with HCIO4 provided the corresponding dications 87 and 88, respectively (Scheme 11) [23,25,51]. Catalytic hydrogenation of calixfurans on Raney nickel, Ru/C, or Ru-Rh/C produces the corresponding caUxtetrahydrofurans, such as 89 [ 18,32]. 

Until now examples for catalytic reactions involving ferrates with iron in the oxidation state of -l-3 are very rare. One example is the hexacyanoferrate 8-catalyzed oxidation of trimethoxybenzenes 7 to dimethoxy-p-benzoquinones 9/10 by means of hydrogen peroxide which was published by Matsumoto and Kobayashi in 1985 [2]. Using hexacyanoferrate 8 product 9 was favored while other catalysts like Fe(acac)3 or Fe2(S04)3 favored product 10 (Scheme 2). The oxidation is supposed to proceed via the corresponding phenols which are formed by the attack of OH radicals generated in the Fe/H202 system. 

Benzoquinone. The formation of cyanocobaltate(II) in a hydrogen atmosphere and in the presence of excess benzoquinone resulted in the absorption of only 40% of that amount of hydrogen normally taken up in the formation of CoH, and the substrate was not catalytically reduced addition of alkali did not activate the system. When excess benzoquinone was added to CoH (H2 atmosphere), hydrogen was not absorbed and, again, alkali did not activate the system. The addition of less than stoichiometric quantities of substrate also resulted in no hydrogen absorption. 

However, when small increments of substrate were added to CoH containing added alkali (KOH, 3X cobalt concentration), 1.4 atoms of hydrogen were absorbed per mole of quinone. This effect of alkali is similar to that noted in the reduction of ferricyanide. However, with benzoquinone, the addition of excess substrate to CoH containing added alkali still resulted in the absorption of hydrogen, the hydrogen atom to substrate ratio being reduced to 0.98. Furthermore, the presence of excess quinone during the formation of cyanocobaltate(II) with added alkali did not prevent catalytic reduction. 

Equation 9 indicates the addition of benzoquinone to CoH to form a new complex which cannot react further with CoH. Equation 10 defines the role of excess alkali in effecting the catalytic reduction of benzoquinone. As shown in previous examples, the hydroxo complex may then undergo the reverse aging process, leading to hydrogen absorption. The over-all result is reduction of benzoquinone to hydroquinone when limited amounts of substrate are available, and to quinhydrone when excess substrate is available. Equation 11 is an attempt to explain the lowered amount of hydrogen absorption noted when cyanocobaltate(II) is prepared in the presence of excess benzoquinone. Displacement of reduced substrate from this binuclear complex by alkali is assumed, since quinone was catalyti-cally reduced when the above procedure was carried out in the presence of added alkali. 

Substrates in the second grouping may be subdivided into those (hydrogen peroxide, ferricyanide, and nitrobenzene) undergoing catalytic reduction only when added to the catalyst in less than stoichiometric quantities in the presence of additional alkali, and those (benzoquinone and benzaldehyde) undergoing catalytic reduction when added in excess quantities in the presence of alkali. Of all these substrates, only hydrogen peroxide has not been studied in the absence of added alkali. Ferricyanide, benzoquinone, and benzaldehyde could be reduced only when alkali was added. Nitrobenzene underwent partial reduction and anthraquinone was quantitatively reduced without requiring additional alkali. 

The addition of excess quantities of hydrogen peroxide, ferricyanide, or nitrobenzene to the catalyst in the presence of added alkali did not result in catalytic reduction, implying that the reverse aging reaction was not the fastest reaction involved similar additions of benzoquinone or benzaldehyde resulted in catalytic reduction, implying that the reverse aging reaction in these cases was the fastest. 

Specifically, two p.-aqua-bridges located in the cleft of the dimer have one hydrogen pointing outward from each side, thus allowing the photo-excited p-benzoquinone (labeled in Scheme 8), but not a bulky 2,5-/-Bu-/ -bcnzoquinone, to enter the cleft and abstract a H radical. This mechanism is consistent with the proposed role of the tyrosyl Yz radical as H abstractor from water [165]. The reaction, however, is not catalytic, because of the irreversible formation of hydroquinone. 

Topaquinone (TPQ), the oxidized form of 2,4,5-trihydroxyphenylalanine (TOPA), is the cofactor of copper-containing amine oxidases. The following model compounds have been prepared in order to understand the catalytic function of TPQ the jV-pivaloyl derivative of 6-hydroxydopamine in aqueous acetonitrile [38] topaquinone hydantoin and a series of 2-hydroxy-5-alkyl-l,4-benzoquinones in anhydrous acetonitrile (o- as well as />-quinones) [39] 2-hydroxy-5-methy 1-1,4-benzoquinone in aqueous system [40] and 2,5-dihydroxy-1,4-benzoquinone [41]. Reaction of model compounds with 3-pyrrolines revealed why copper-quinopro-tein amine oxidases cannot oxidize a secondary N [42], The studies clearly showed that certain model compounds do not require the presence of Cu for benzylamine oxidation whereas TPQ does [38,40] the aminotransferase mechanism proceeds via the -quinone form [39] the 470 nm band can be ascribed to a 71-71 transition of TPQ in />-quinonic form with the C-4 hydroxyl ionized but hydrogen bonded to some residue [40] hydrazines attack at the C-5 carbonyl, forming an adduct in the azo form [41], Electrochemical characterization has been carried out for free TPQ [43],... 

Use of transition metal catalysts opens up previously unavailable mechanistic pathways. With hydrogen peroxide and catalytic amounts of methyl trioxorhe-nium (MTO), 2-methylnaphthalene can be converted to 2-methylnaphtha-l,4-qui-none (vitamin K3 or menadione) in 58 % yield and 86 % selectivity at 81 % conversion (Eq. 10) [43, 44]. Metalloporphyrin-catalyzed oxidation of 2-methylnaphtha-lene with KHSOs can also be used to prepare vitamin K3 [45]. The MTO-catalyzed process can also be applied to the synthesis of quinones from phenols [46, 47]. In particular, several benzoquinones of cardanol derivatives were prepared in this manner [48], The oxidation is thought to proceed through the formation of arene oxide intermediates [47]. 

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