Dehydrogenations 2,3-dichloro-5,6-dicyano- 1,4-benzoquinone

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... 

The oxidation (dehydrogenation) of the EDOT-dimer by quinones like chloro-anil or 2,3-dichloro-4,5-dicyano-benzoquinone (see Figure 5.17) presents a rapid and easy access to the bis-EDOT (BEDOT) 2,2 -di(3,4-ethylenedioxythiophene), ... 

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 dihydrodiazepine 3 obtained from diaminomaleonitrile and A. A -dimethylacrylamide is dehydrogenated to the diazepine 4 by 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ).186... 

Quinones, which become reduced to the corresponding hydroquinones. Two important quinones often used for aromatizations are chloranil (2,3,5,6-tetrachloro-1,4-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 °... 

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>. 

Other dehydrogenation agents include sulfur, selenium dioxide, palladium on charcoal, and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ). Some reactions proceed spontaneously. Dehydrogenation also occurred... 

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. 

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). 

This PTE film was then dehydrogenized using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to produce a PTV film. Eigure 17 shows the conversion scheme. 

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. 

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]. 

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