2.3- Dichloro-5,6-dicyano-1,4-benzoquinone, dehydrogenation with

Isopropenylbenzofuran (124, Scheme 30) affords good yields of the adducts 123 and 125 on separate reaction with maleic anhydride and tetracyanoethylene. With but-3-en-2-one, 2-isopropenylbenzofuran (124, Scheme 31) affords the adducts 126 and 127 in a combined yield of 29%. When the crude product was dehydrogenated with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in boiling benzene, the aromatized product 128 (6%) was obtained. It was accompanied by the dicyanodibenzofuran 129, which was found to arise from the excess diene present in the reaction mixture. A speculative mechanism is shown. 

Various alkylcyclopropanes have been converted to (l-alkenyl)cyclopropanes by dehydrogenation with trimethylsilyl triflate, selenium dioxide,tetrachloro-1,4-benzoquinone, 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, di-/er/-butyl dicarbonate and potassium tert-butoxide/dimethyl sulfoxide. A related transformation is the Ramberg-Back-lund reaction of bis(l-trimethylsilylcyclopropylmethyl) sulfone which gave ( )-l,2-bis(l-trimethylsilylcyclopropyl)ethene in fair yield. ... 

Dehydrogenation of some aromatic steroids with 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ) affords styrene analogues. Neoergosterol (252) gives the 14-ene (253) rapidly at room temperature, and is more slowly transformed into the 14,16-diene (254). The first step provides a further illustration of the... 

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... 

Dehydrogenation is a rarely used method for the production of fully unsaturated azepines, and there are no examples of its use for the formation of simple monocyclic systems, although 3-hydroxy- and 3-methoxy-2//-azepin-2-ones can be obtained by dehydrogenation of the corresponding l,5-dihydro-2//-azepin-2-ones with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in benzene in a sealed tube at 100 48-51-52-67... 

The 1H—NMR spectrum of 5,6,17,18-tetrahydro[2.2](2,7)phenan-threnopane (48) is compatible with the dihydrophenanthrene units being in an anti position. Dehydrogenation of 48 with 2,3-dichloro-5,6-dicyano-p-benzoquinone in benzene gave [2.2](2,7)phenanthrenophane which, owing to the similarity of its 1H—NMR spectrum to that of 2,7-dimethyl-phenanthrene, is assumed to have its phenanthrene units in the anti position 71>. 

Ebel s method is an adaptation of the Stoermer synthesis of benzo-[h]furans and involves the 0-alkylation of a phenolate anion (229, Scheme 58) with a 2-halocyclohexanone (230). The resultant 2-phenoxycyclo-hexanone 231 is then cyclized by poly phosphoric acid, usually at 100°C, or sometimes by concentrated sulfuric acid, to afford a 1,2,3,4-tetrahydrodi-benzofuran (232). Dehydrogenation to the dibenzofuran is often effected with palladized charcoal, but 2,3-dichloro-5,6-dicyano-l,4-benzoquinone ... 

Subsequent ring closure with ammonia, hydrogenation using PtO2/H2 or Pd-C/H2 [32], DCC/HOBt-mediated amidation with t-butyl amine, followed by dehydrogenation using benzeneseleninic anhydride or 2,3-dichloro-5,6-dicyano-l, 4-benzoquinone (DDQ)/bis(trimethylsilyl)-trifluoroacetamide (BSTFA) [33] combination afforded 4. 

Bamford-Stevens reaction of the tosylhydrazones of the readily available tetrahydrofuran-3-ones provides a useful synthesis of 2,3-dihydrofurans which may be dehydrogenated to furans with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (66CJC1083). Tetrahydrofuran-2-ones (y-butyrolactones) may be alkylated in the 3-position with LDA and an alkyl halide. The products on reaction with phenyl selenylchloride and LDA, and subsequent oxidation, yield 3-alkylfuran-2(5//)-ones reducible with DIBAL to furans (75JOC542). 

A synthesis of 277-pyrroles has been reported, relying on reductive annulation of 7-nitroketones (Scheme 1), as exemplified by the transformation of the substrate 7 into the pyrrolidine 8, which was eventually dehydrogenated to the 277-pyrrole 9 by treatment with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) <2003TL3701>. 

The elements sulfur and selenium, which combine with the hydrogen evolved to give, respectively, H2S and H2Se. Little is known about this mechanism either. Quinones, which become reduced to the corresponding hydroquinones. Two important quinones often used for aromatizations are chloranil (2,3,5,6-tetrachloro-l,4-benzoquinone) and DDQ (2,3-dichloro-5,6-dicyano-l,4-ben-zoquinone). The latter is more reactive and can be used in cases where the substrate is difficult to dehydrogenate. It is likely that the mechanism involves a transfer of hydride to the quinone oxygen, followed by the transfer of a proton to the phenolate ion ... 

Dehydrogenation of pyrimido[4,5-d]azepines 532,540 (R = Ph), 543, and 548 (R = Ph) was unsuccessful over palladium-on-carbon catalyst in boiling decalin or with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in boiling dioxane. However, when pyrimido[4,5-6] azepine 549 was treated with palladium-on-carbon catalyst, dihydropyrimido[4,5-6]azepines 551 and 552 could be isolated chromatographically in 10 and 5% yields, respectively (78H275). When pyrimido[4,5-6]azepine 549 was heated in dioxane in the presence of DDQ, 5,6-dihydropyrimido[4,5-overall yield when pyrimido[4,5-carbon tetrachloride, and the resulting bromohydrin 553 was reduced with zinc powder in acetic acid at 60°C. Acetylation of the bromohydrin with acetic anhydride in pyridine gave the more stable acetoxy derivative 554. 

The dehydrogenating agent 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) is prepared from 2,3-dichloro-5,6-dicyanohydroquinone by oxidation with lead dioxide [431] or dinitrogen tetroxide [457] (equation 317). 

This high-potential quinone is second in effectiveness to 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in the dehydrogenation of tetralin, acenaphthene, and dibenzyl in benzene at SO"." Kinetic studies are reported. The dehydrogenation of the 1,1-dimethyltetralin is attended with Wagner-Meerwein rearrangement ... 

For synthesis decumbenine B, compound 2-14 was condensed with 2-7 in THF with LDA (lithium diisopropylamide) at -70°C followed by deprotonation with dilute hydrochloric acid. The desired intermediate 2-15 was obtained successfully in 49% yield. Lithium aluminum hydride reduction of 2-15 afforded the amine 2-16, which was converted to 2-17 by debenzylation with palladium on charcoal in acetic acid. The final step was dehydrogenation, after comparison with several reagents including palladium on charcoal in acetic acid and DDQ (2,3-dichloro-5,6-dicyano-l,4-benzoquinone)/l,4-dioxane, the best results were obtained by using DDQ/benzene. The yield of decumbenine B was 41% (Scheme 3). 

A. Coupling reaction using ferric chloride (FeCl ) as oxidant 1, The polymerization from homo-monomer Compound 16 isolated from Vitis amurensis showed strong biological activity [7, 65] and its biomimetic synthesis was achieved as shown in Fig. (7). Oxidative coupling reaction of 1 with FeCU as oxidant produced an intermediate, ( )- -viniferin (107), by silica gel column chromatography. After acetylation, it was dehydrogenated by treatment with 2,3-dichloro-5,6- dicyano-1, 4-benzoquinone (DDQ) to afford an intermediate(108) and the desired compound 16 in 20% yield [7]. 

Euxylophorine D (85). On the basis of analogous spectroscopic behavior and co-occurrence with (84), structure (85) was proposed for this alkaloid. This proposal was confirmed by partial synthesis of (85) via dehydrogenation of (84) with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone. 

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