Diquinone

A facile way of promoting the cyclization is to increase the nucleophilicity of the aryl system when possible. In the total synthesis of diazadiquinomycins A and B, for example, the authors were able to effect a double Knorr cyclization with concomitant in situ oxidation to the internal diquinone 23 by deprotecting the hydroquinone thereby lowering the activation barrier for the desired transformation. If the hydroquinone is left protected as the di-MOM ether, the reaction does not take place. ... 

Liu, H. Qin,Z. Thatcher, G. R. Bolton, J.L. Uterine peroxidase-catalyzed formation of diquinone methides from the selective estrogen receptor modulators raloxifene and desmethylated arzoxifene. Chem. Res. Toxicol. 2007, 20, 1676-1684. 

Beer PD, Timoshenko V, Maestri M et al (1999) Anion recognition and luminescent sensing by new ruthenium(II) and rhenium(I) bipyridyl calix[4]diquinone receptors. Chem Commun... 

The diquinone 300 has been shown to react with a variety of primary amines producing carbazole quinones 301, a process which presumably involves an intermediate such as 302 formed by Michael-type addition. Alkyl-, aryl-, and heteroarylamines and amino acids have been utilized. The reaction failed with p-nitro- and p-acetylanilines neutral and acidic amino acids required base catalysis. Hydroxyl-... 

Diphenyl-diquinone-3,4,3, 4 -bis-diazide (4,4 ) see 4,4 -Bis (diazo)-3,3 -dioxy-biphenyl 2 B139... 

PPO (known also as catecol oxidase, phenolase or diphenol-oxygen oxidereductase) and POD catalyse the oxidation of o-diphenols to o-diquinones, as in the hydroxylation of monophenols [13]. PPO is located exclusively in the plastids of healthy tissues, while most phenolic compounds are localized in the vacuoles, the two compounds thus being physically separated [13]. 

A number of "binaphthyldiquinones" have recently been found as natural products, and Russian workers have described a very simple, one-step method for preparation of the basic system. Thus, diquinone la was obtained in 40% yield simply by heating a solution of 1,4-naphthoquinone with two equivalents of sodium hydride in THF. Use of 2-chloro- or 2-bromo-1,4-naphthoquinone gave the diquinones lb and lc in 94 and 92% yield respectively. 

Oxidation of benzo-fused 1,3-dioxepane 79 with cerium ammonium nitrate afforded the />-diquinone 80 <2006T635>, and oxidation of 2-hydroxydioxepin 81 with manganese dioxide gave l,3-dioxa-4-cyclohepten-6-one 82 <2004RJ01830> (Scheme 14). 

Taking into account om calix[4]tube ligand design10, the novel bis-calix[4]diquinone receptors were prepared via the initial synthesis of various bis-calix[4]arene derivatives connected by alkylene chain units and subsequent oxidation of the remaining phenolic... 

Similar structures 37 and 38, bearing ureido functions on the lower rim of calix[4]diquinone or monoquinone moieties, were used for anion recognition with the aid of electrochemistry (cyclic voltammetry) [47,48]. Some of these compounds were found [49] to bind selectively HSOj or H2POj anions. 

Two ureido functions introduced into the upper rim of calix[4]arene [52] or the corresponding calix[4]diquinone derivative 41 exhibit good complexa-tion abilities for various anions. Even in highly competitive solvents such as DMSO-d6, quinone 41 shows [53] very strong complexation for H2POj (K4l= 13,900 M-1) or for benzoate (K41=2,430 M-1). The complexation process can be observed using electrochemical methods (cyclic voltammetry) where the addition of anions generates substantial cathodic shifts. 

The Ru(II)bipyridylcalix[4]diquinone receptor 43 selectively binds and senses acetate anions (from H NMR titrations in DMSO-d6 solution K= 9,990 M1) [37]. This receptor exhibited only weak luminescence because calix[4]diquinone is an electron acceptor, quenching the [Ru(bpy)3]2+ emission... 

Photoinduced intramolecular electron tunneling was observed also in some other porphyrin containing bridge molecules, such as porphyrin covalently linked to phenolphthalein [308], dimethylaniline — mesoporphyrin II — quinone triad [309], Zn porphyrin-viologen-quinone triad [310], carotenoid — porphyrin -diquinone tetrad [311]. The influence of conformational state of porphyrin-viologen bridge molecules on the rate of PET reactions was studied in Ref. [312]. 

Diquinone isomeric derivatives 71a and 71b can serve as examples of the A—D—A motif [119]. Interestingly, although both derivatives contain weak donors and weak acceptors moieties, they do give segregated stack-... 

Triptycene diquinone derivatives, (IV), prepared by Hua (5) were effective in inhibiting nucleic acid or protein syntheses and used in the treatment of multidrug-resistant tumor cells. 

Oxidation of hydroquinones. Hydroquinones are oxidized to quinoncs in high yield by treatment with CAN for a few minutes in aqueous acetonitrile. The method is applicable to the production of o-, p-, and diquinones. 

A further example of steric control on electron transfer processes involving calixarene hosts has been provided by Ziessel and coworkers who appended one (56) or two [Ru (bpy)3] moieties and a/ac-[Re Cl(CO)3(bpy)] (57) to a calix[4]diquinone [95]. For all the complexes the luminescence quantum yield is very low because of... 

The bisquinone 70 was obtained by condensation of 2-anilino-3-chloro-1,4-naphthoquinone with sodium sulfide and 2,3-dichloro-l,4-naphthoqui-none. The product, a pentacyclic thiazine, lost sulfur upon heating to give 70. This diquinone can be reduced with SnCl2 and subsequent oxidation with air yielded the monoquinone 71 (23CB1291). 

---