Benzo Benzoquinone

Cyclic conjugation is continuous in o-benzoquinone and discontinuous in p-benzoquinone (Scheme 15, cf. Scheme 4). The donors (the C=C bonds) are on one side of the cyclic chain and the acceptors (the C=0 bonds) are on the other side in o-benzoquinone. In p-benzoquinone the donors and the acceptors are alternatively disposed along the chain. The thermodynamic stability of o-benzo-quinone is under control of the orbital phase property. The continuity conditions are not satisfied. o-Benzoquinone is antiaromatic. The thermodynamic stability of p-benzoquinone is free of the orbital phase (neither aromatic nor antiaromatic) and comes from the delocalization between the four pairs of the neighboring donors and acceptors. In fact, p-benzoquinone, which melts at 116 °C, is more stable than o-benzoquinone, which decomposes at 60-70 °C. 

Benzo(b)fIuoranthrene la 39, 85 Benzo(k)fluoranthrene la 39, 86 Benzo(ghi)perylene la 39,85 Benzophenone derivatives lb 282 Benzo(a)pyrene la 39,85,103 p-Benzoquinone derivatives la 72 Benzothiazoles lb 237 Benzoyl chloride la 70 Benzoylecgonine lb 32,34,35 3,4-Benzpyrene la 60 Benzthiazide lb 188 Benztriazole, 2-(2-hydroxy-5-methyl-phe-nyl)- la 282... 

Similarly, 1-vinylcyclohexane can be trapped with dimethyl acetylenedicarboxylate in refluxing xylene to afford 195 in 78% yield (equation 126) . Benzo[ ]anthracene can be obtained by the reaction of 196 and 1,2-dihydronaphthalene (equation 127) and oxidation of 197 with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone . 

The generation and trapping of 5,6-bis(trimethylsilyl)benzo[c]furan 126 was reported by Wong utilizing Warrener s s-tetrazine methodology. The trapping of the silylated isobenzofuran with A-phenylmaleimide is illustrated below. A number of other dienophiles such as dimethyl acetylenedicarboxylate, benzoquinone, naphthoquinone and anthra-l,4-quinone have also been used <00TL5957>. 

Commercially available 2,3-dichloro-5,6-dicyano-l,4-benzo-quinone was employed. 1,6-Methano[10]annulene was obtained in equally good yields, when 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, prepared by the method of Walker and Waugh,4 was utilized. 

Since a2 + b2 > 2ab for all positive values of a and b, except a = b 0, we conclude that S, 3 (ortho) > S 3 (para). Consequently, the pi LUMO of ortho benzo-quinone will be lower in energy than the pi LUMO of para benzoquinone. Furthermore, the degeneracy of the oxygen lone pair AO is lifted more in the case of ortho benzoquinone. The final conclusion is that the mr transition is predicted to occur at longer wavelengths in the ortho isomer relative to the para isomer. 

The palladium(II)-mediated oxidative cyclization is also applied to the synthesis of carbazole-l,4-quinone alkaloids. The required arylamino-l,4-benzo-quinones are readily prepared by arylamine addition to the 1,4-benzoquinone and in situ reoxidation of the resulting hydroquinone [131]. 

Addition of the arylamines 117 to 2-methoxy-3-methyl-l,4-benzoquinone 118 affords regioselectively the 5-arylamino-2-methoxy-3-methyl-l,4-benzo-quinones 119 (Scheme 37). Palladium(II)-catalyzed oxidative cyclization leads to the carbazole-l,4-quinones 28 [135,136],previously obtained by the iron-mediated approach (cf. Scheme 14). Regioselective addition of methyllithium to the quinones 28 provides carbazomycin G 29a and carbazomycin H 29b [96,135]. Reduction of 29a with lithium aluminum hydride followed by elimination of water on workup generates carbazomycin B 23a [135]. Addition of heptylmag-... 

Ether cleavage of 4-heptyl-3-methylveratrole 121 using boron tribromide affords 4-heptyl-3-methylcatechol 122 (Scheme 38). Oxidation of the catechol 122 with o-chloranil to 4-heptyl-3-methyl-l,2-benzoquinone 123 and subsequent immediate addition of aniline leads to 5-anilino-4-heptyl-3-methyl-l,2-benzo-quinone 124. Unlike the very labile disubstituted ort/zo-quinone 123, compound 124 is stable and can be isolated. Palladium(II)-mediated oxidative cyclization of the anilino-l,2-benzoquinone 124 provides carbazoquinocin C 51. 

Synonyms AI3-09068 AIDS-153 B 1266 1,4-Benzoquine Benzoquinone Benzo-l,4-quinone 1,4-Benzoquinone p-Benzoquinone BRN 0773967 Caswell No. 719C CCRIS 933 Chinone Cyclohexadienedione 1,4-Cyclohexadienedione 2,5-Cyclohexadiene-l,4-dione 1,4-Cyclohexa-diene dioxide 1,4-Dioxybenzene EINECS 203-405-2 EPA pesticide chemical code 059805 NCI-C55845 NSC 36324 Quinone 4-Quinone RCRA waste number U197 UN 2587 USAF P-220. 

Benzoquine, see p-Quinone Benzoquinol, see Hydroquinone Benzoquinone, see p-Quinone Benzo-l,4-quinone, seep-Quinone... 

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 ... 

Benzophenone, perhydroazepine, 58, 120 Benzophenone, piperidine, 58, 119 3/f-2-Benzopy raii-3-one, l,4-dihydro-6,7-dimethoxj, 55, 45 Benzo[a] pyrene, 58, 15, 16 p-Benzoquinone, 55, 43... 

Unexpected reactions occur when benzo[c]furans are treated with o-quinones. Tedder and co-workers reacted 5,6-dimethyl-l,3-diphenyl-benzo[c]furan (210) with o-benzoquinone (211, X = H) and o-chloranil (211, X = Cl) to give dioxoles (212). Subsequent investigations have shown that [714 + 7i4]-cycloadducts (213) are also formed other benzo[t]furans... 

Furo[3,4-J]pyridazines have also been used in Diels-Alder reactions (331a with maleic anhydride, acrylic acid, 1,4-naphthoquinone, dibenzoyl-ethylene, 1,4-benzoquinone, benzo[c]furandione ° 331c with maleic anhydride) 331a has been shown to be more reactive than 331c. 1,3-Diphenylfuro[3,4-b]quinoxaline (335) has been obtained from phthalide 334 (Eq. 17) as a green crystalline, quite stable solid (mp 244-246°C). In DMSO (deep blue solution), 335 reacts instantaneously with such dienophiles... 

Routes to benzo-fused derivatives of 1,4-dioxanes, 1,4-oxathianes and 1,4-dithianes make use of anions or dianions of the appropriate 1,2-disubstituted benzene. An alternative approach to the synthesis of 1,4-benzodioxanes involves Diels-Alder addition reactions of alkenes across the quinone function of 1,2-benzoquinones, e.g. (352) — (353). 

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