2,3-dichloro-5,6-dicyano-l,4-benzoquinone DDQ

The next major obstacle is the successful deprotection of the fully protected palytoxin carboxylic acid. With 42 protected functional groups and eight different protecting devices, this task is by no means trivial. After much experimentation, the following sequence and conditions proved successful in liberating palytoxin carboxylic acid 32 from its progenitor 31 (see Scheme 10) (a) treatment with excess 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in ie/t-butanol/methylene chloride/phosphate buffer pH 7.0 (1 8 1) under sonication conditions, followed by peracetylation (for convenience of isolation) (b) exposure to perchloric acid in aqueous tetrahydrofuran for eight days (c) reaction with dilute lithium hydroxide in H20-MeOH-THF (1 2 8) (d) treatment with tetra-n-butylammonium fluoride (TBAF) in tetrahydrofuran first, and then in THF-DMF and (e) exposure to dilute acetic acid in water (1 350) at 22 °C. The overall yield for the deprotection sequence (31 —>32) is ca. 35 %. 

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... 

Benzyloxybenzylamine (BOBA) 48 is a new class of an amine support and was prepared from Merrifield resin in two steps [56]. BOBA resin was treated with an aldehyde in the presence of an acid to give an imine that subsequently reacted with Yb(OTf)3-catalyzed silyl enolates (Scheme 18). Cleavage with trimethylsilyl triflate (TMSOTf) or 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) gave either phenols or amines, respectively. 

EPR techniques were used to show (Polyakov et al. 2001a) that one-electron transfer reactions occur between carotenoids and the quinones, 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ), and tetrachlorobenzoquinone (CA). A charge-transfer complex (CTC) is formed with a -values of 2.0066 and exists in equilibrium with an ion-radical pair (Car Q ). Increasing the temperature from 77 K gave rise to a new five-line signal with g=2.0052 and hyperfine couplings of 0.6 G due to the DDQ radical anions. At room temperature a stable radical with y=2.0049 was detected, its... 

Acyl-substituted quinolizinium ylide 63 was obtained by treatment of its 1,2-dihydro analogue with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ). Its 1,3-dipolar cycloaddition with an acetylenic ester in excess was regioselective and was accelerated in polar solvents yielding the intermediate adduct 64 and finally the corresponding cyclazine 65, as shown in Scheme 2 <2001JOC1638>. 

The fullerene C o was used as the Unking agent for the synthesis of (PCHD-fc-PS)6 and (PS-fc-PCHD)6 star-block copolymers [154], The polymers were then aromatized with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, DDQ, in 1,2-dichlorobenzene to yield the corresponding copolymers containing poly(l,4-phenylene) blocks. In order to achieve high 1,4-isomer contents and to avoid termination reactions, the polymerization of CHD was conducted in toluene at 10 °C without the presence of any additive to yield products with low molecular weights. Coupling of the PCHD-fo-PSLi to C60... 

In Grigg s approach to hippadine (37), he established the connection between the two phenyl rings via the Stille-Kelly reaction [45]. When diiodide 35 was submitted to the Pd(0)/ditin catalyst system, the intramolecular cyclization was realized to establish the C—C bond in lactam 36. Oxidation of the indoline moiety in 36 using 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) then delivered hippadine (37). Analogously, the intramolecular Stille coupling of dibromide 38 led directly to hippadine (37) [46]. 

A solution of 100 mg. (0.41 mmole) of 4,4 -dimethoxybibenzyl (Note 1) in 1.5 ml. of anhydrous dioxane (Note 2) was placed in a 10-ml. round-bottomed flask. To this was added 103 mg. (0.45 mmole) of 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ Note 3) dissolved in 1.5 ml. of anhydrous dioxane. The flask was fitted with a reflux condenser and heated in an oil bath at 105° for 18 hours. The solution, which was initially deep green, became pale yellow as the hydroquinone crystallized out. The mixture was cooled, and the solid was filtered off. It was washed with 1 ml. of warm benzene followed by 6 ml. of warm chloro-... 

For the first time, application of sequential Diels-Alder reactions to an in situ-generated 2,3-dimethylenepyrrole was shown with various dienophiles 548 to afford 2,3,6,7-tetrasubstituted carbazoles (549). This novel tandem Diels-Alder reaction leads to carbazole derivatives in two steps, starting from pyrrole 547 and 2 equivalents of a dienophile, and is followed by 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) oxidation of the intermediate octahydrocarbazole. Mechanistically, the formation of the intermediate octahydrocarbazole appears to involve two sequential [4+2] cycloadditions between the exocyclic diene generated by the thermal elimination of acetic acid and a dienophile (529) (Scheme 5.17). 

Since the publication of CHEC-II(1996), there have been very few examples related to the reactivity of substituents attached to ring carbon atoms. One case involves the reaction of 3-benzylidene-2,3-dihydro-2-methyl-l,2-benzothiazin-4-one 1,1-dioxide 163 with the alkylidenephosphorane derived from salt 164 forming the tricyclic-fused ring compound 165 (Scheme 20) <1996J(P1)2541>. This material 165 was oxidized with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) affording the biphenyl 166. Ring-opened product 167 was produced from 165 upon exposure to />-toluene-sulfonic acid and heat. 

Hurd-Mori reaction on hydrazone 147 produced methyl thieno[3,4-r/ -l,2,3-thiadiazole-6-carboxylate 148 along with methyl thieno[3,2-r7 -l,2,3-thiadiazole-5-carboxylate 135 and methyl 5,6-dihydrothieno[3,2-r7 -l,2,3-thiadiazole-5-carboxylate 149 in a ratio of 1 2.6 0.5 (72% combined yield). Conversion of compound 149 to the fully aromatized 135 is accomplished by treatment with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in refluxing benzene for 10 days (Scheme 15). A modified reaction mechanism for the Hurd-Mori reaction is also presented here <1998H(48)259>. 

Several examples of the reactivity of nonconjugated rings were reported in <1996CHEC-II(7)921>. The main reactivity appears to be by conversion into the aromatized product. For example, removal of the carbamate group in 56 and subsequent oxidation with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) affords the aromatized product 57 (Equation 6) <1996H(43)447>. 

Studies directed toward the synthesis of bicyclomycin have resulted in the discovery of efficient routes to the construction of the 2-oxa-8,10-diazabicyclo[4.2.2]decane system (160). Thus, the monolactim ether (155) with a hydroxypropyl side chain at position 3, on oxidation with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ), gave the product (156) in good yield, presumably via an iminium species (Scheme 51). No trace of the spiro compound (157) could be detected in this reaction. The formation of (156) is probably kinetically controlled. Prior protection of the alcohol as a silyl ether, followed by DDQ oxidation, gave the pyrazinone (158) subsequent deprotection and acid treatment gave the thermodynamically preferred spiro compound (159). The method has been extended to the synthesis of (160), having an exocyclic methylene this compound is a key intermediate in the total synthesis of bicyclomycin [88JCS(P1)2585]. 

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. 

The key to the construction of the system is the choice of the quinone redox couple in the oil phase and the oil itself. The quinone compound must be reduced by Fe(II) ions, and the reduced form must be oxidized by bromine. These requirements indicate that the redox potential must be in the range between 0.77 and 1.07 V vs. NHE. After investigating of many redox compounds, we found that 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) dissolved in n-butyronitrile may be a good candidate for the system. DDQ has a largely positive redox potential because of its strong electron withdrawing substituents. 

Treatment of imidazo[2,l-A [l,3,5]benzotriazepines 79 with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in acetonitrile at ambient temperature resulted in oxidative ring contraction with formation of stable (dihydroimidazo-lybbenzimidazoles 80 (Scheme 15). The reaction was suggested to occur via the initial hydride abstraction from N(6) followed by triazepine ring scission and formation of nitrenium ion <2005FA127>. 

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