Tetrachloro-o-benzoquinone

DDQ has proved to be the most versatile of the high-potential quinones although certain others, notably chloranil (previous section) and tetrachloro-o-benzoquinone have been used on occasion. 

Recently Swan has employed tetrachloro-o-benzoquinone in the oxidation of the 3,4-dihydro-j8-carbolinium cation 124 to the j8-carbo-linium cation 252. Dehydrogenation with palladium black at 175° or at a higher temperature and with selenium has also been successfully used for the purpose. 

The allylidenephosphorane (64) with phenanthraquinone gave the pyran (65) together with small amounts of (66) and (67). Similar pyrans were also obtained from (64) and a-naphthoquinone and tetrachloro-o-benzoquinone. 

The reactivity of stable germaphosphenes has been previously investigated and reviewed.3,4,7 The chemical behavior of Mes2Ge = PAr 155 toward orthoquinones (tetrachloro-o-benzoquinone, 3,5-di-terr-butyl-o-benzoqui-none, and 1,2-naphthoquinone) and ce-diketones (benzil and biacetyl) has been examined. The reaction with o-quinones involved probably radical intermediates, and in each case only the less encumbered isomer of the corresponding [2 + 4] cycloadduct 156 was formed. Benzil led in a very similar manner to a l,4,2,3-dioxagermaphosphin-5-ene 157, whereas, as was observed with acetone, an ene-reaction occurred with biacetyl to afford 158138 (Scheme 29). 

HjCat represents catechol or hydroquinone, Q quinone, SQ semiquinone anion, HCat- catechol monoanion, and Cat2 catechol dianion DTBQ represents 3,5-di-rerr-butyl-o-quinone, o-Q o-benzoquinone, p-Q p-benzoquinone, TCQ tetrachloro-o-benzoquinone, and TFQ tetrafluoro-o-benzoquinone. 

Some reactions of munchnones occur via acylamino ketenes, the covalent valence tautomers of the betaines. The ketenes are intermediates in the thermolysis (see Scheme 22) and in the formation of azetidinones from imines (equation 69) they are thought to be involved in the aminolysis of the mesoionic compounds, which results in amides of a-acylamino acids, and in the formation of the benzodioxin (247) by the combined action of acetic anhydride and tetrachloro-o-benzoquinone on Af-benzoylalanine (equation 70). 

Thioesters of methylarsenic(III) acid and an equimolar amount of tetrachloro-o-benzoquinone give unsymmetrical compounds (XXIX) (73) ... 

Compounds of type XXIX are stable at room temperature but on heating rearrange to symmetrical compounds of type XXIX. When a second equivalent of tetrachloro-o-benzoquinone is added, the As—S bonds are oxidized, yielding symmetrical compounds of type XXVIII and disulfides. 

The reaction of 3-(2-bromoethyl)indole (284) with 2-chloropyridine gave indoloquinolizine 285, which was dehydrogenated with tetrachloro-o-benzoquinone to yield indoloquinolizinium salt 286 (62JA3393 68CPB549). 

Bicvclic and Tricyclic Phosphoranes The first synthesis of a series of pentaco-ordinated structures (82a-d) containing a three-membered (phosphirene) ring has been achieved by the oxidative addition of tetrachloro-o-benzoquinone... 

Aliphatic and aromatic thiols have been added to (5) -methylphenylvinylphosphine oxide (84) to provide optically active P-alkylthio- and p-arylthioethylphenylphosphine oxides (85).The reaction of the phosphine sulphide (86) with tetrachloro-o-benzoquinone gives (87) which undergoes further rearrangement. ... 

Very selective oxidizing agents suitable for the conversion of primary alcohols into aldehydes are high-potential quinones such as tetrachloro-o-benzoquinone, tetrachloro-p-benzoqninone, and 2,3-dichloro-5,6-dicyano-p-benzoquinone [973]. Such dehydrogenations are carried out in chloroform, carbon tetrachloride, or ethanol, usually under very mild conditions at room temperature or in refluxing ether, and give fair to good yields (equation 216) [973]. 

With tetrachloro-o-benzoquinone 1,2-benzodithiolethione gives a spirane (163).236 4-Phenyl-l,2,4-triazoline-3,5-dione forms mesoionic compounds (e.g., 164) with l,2-dithiole-3-thiones.237-238... 

Treatment of pentachlorophenol (590) with NH4N03-(CF3C0)20 in CH2CI2 resulted in the predominant formation (80%) of tetrachloro-o-benzoquinone 591 (Scheme 111). 

The reaction of ( )-bis-(2,4,6-tri-t-butylphenyl)diphosphane (16) with a four equivalent excess of tetrachloro-o-benzoquinone (17) gave (19). Evidence was presented to suggest that the reaction occurred via (18) with cleavage of the P=P bond and indeed, with two equivalents of (17) a low yield of (18) was isolated. The structures of the products were determined by X-ray crystallography and it was also suggested that the formation of (18) involved an electron transfer mechanism (Route A or Route B, Scheme 1) via a phosphinium radical cation and the radical anion of (17). ... 

On prolonged heating with 2,3-dimethylbutadiene compounds (38) form the cycloadducts (44). Tetrachloro-o-benzoquinone adds in the same way but much more quickly in a subsequent reaction a second molecule adds to the phosphorus atom <83TL548i>. 

The photoaddition of sulfur dioxide to o-quinones in benzene solution to produce cyclic sulfates (26) in fair to high yields was reported by Schenck and Schmidt-Thomee 1431 in 1953. Products were obtained from tetrachloro-o-benzoquinone, 1,2-naphthoquinone, 3-nitro-l,2-naphtho-... 

A lesser degree of loss of configuration was observed in the reactions of cis- 36> and iraMS-stilbene 35> with tetrachloro-o-benzoquinone to give dioxenes. The m-stilbene reaction (in acetone or acetonitrile) afforded about 80% of cis-adduct while 88% of trans-a.d6.net 35> was obtained from the reaction of trans-stilbene (both reactions at 15°, A >400 nm). Curiously, irradiation of the quinone and cfs-stilbene (or diphenyl-acetylene) in benzene solution produced the mono-phenyl ether (33)... 

Photochemistry of diones began with Klinger s 82> report of the sunlight reactions of benzil and phenanthrenequinone with diethyl ether but reactions of diones with ethers have been investigated to a very limited extent since then. The reported reactions include biacetyl (dioxane 20>), benzil (diethyl ether 82>, dioxane 128>), tetramethyltetralindione (73, dioxane 60>), tetrachloro-o-benzoquinone (dioxane 128>), acenaphthene-quinone (dioxane 128>) and phenanthrenequinone (diethyl ether 82>, di-isopropyl ether 127>, di-n-butyl ether 127>, tetrahydrofuran 128>, dioxane 128>, anisole 128>, methoxycholestane (86) 128>, methoxy-5-cholestene 128>). 

The reaction of biacetyl and dioxane was complex affording modest yields of 1,2-adduct, diketopinacol 63, acetyldioxane, and compound 91 whose origin is obscure. Benzil in diethyl ether furnished benzilbenzoin (63) a mixture from which no pure products were isolated was obtained with dioxane. A similar result was obtained with acenaphthenequinone and dioxane. Tetrachloro-o-benzoquinone and dioxane afford 20% of a 1,4-adduct analogous to 87 the remaining products were not characterized. 

A similar result has been observed 36> in reactions of tetrachloro-o-benzoquinone in benzene solution where the phenyl ether 33 was isolated. The reaction reportedly required cis-stilbene or diphenylacetylene and proceeded extremely slowly in their absence. 

Tetrachloro-o-benzoquinone. Photodecarbonylation of an a-Diketone. Chem. Commun. 1702 (1968). 

Sulfines, although not so reactive as sulfenes, have the advantage of being able to participate in Diels-Alder reactions. Xanthenethione 5-oxide (314) and thiofluorenone 5-oxide (317) undergo [4 4- 2] cycloaddition with the diene equivalent, tetrachloro-o-benzoquinone (315), to form the 1,4,2-dioxathiane 5-oxides (316) and (318) (Scheme 47) <67RTC64l>. 

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