Chloranil oxidants

Chloranil oxidation. To 17.86 g of a suspension of the leuco-l,4-bis[2-(2-hydroxyethylamino)ethylamino]-5,8-dihydroxyanthraquinone (0.03 mole) in 2-methoxyethanol was added gradually with stirring 15 ml of 8 N ethanolic hydrogen chloride. The system was chilled with an ice bath and stirred as 7.50 g (0.0305 mole) of chloranil powder was gradually added. The mixture was stirred overnight at room temperature and diluted with 600 ml of ether. The solid was collected and washed with tetrahydrofuran. Yield of l,4-bis[2-(2-hydroxyethylamino)ethylamino]-5,8-dihydroxyanthraquinone dihydrochloride 21.34 g, melting point 203-205°C (without recrystallisation). 

Kang and coworkers76 have also used organic electron acceptors such as 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and chloranil. A solvent effect was observed when polymerization was carried out using DDQ. Polymerization in acetonitrile gave the lowest conductivity, and in water it was slightly better. A similar solvent dependence was observed for chloranil oxidations. 

Chloranil oxidized a variety of methylarsenic(iii) esters, amides, or cyclic thioesters, products such as (89), for example, being obtained from a dithioester of methylarsonous acid. ° The analogous reaction with 2-iodo-l,3,2-dihetero-arsolans, however, proceeded with simultaneous cleavage of the As—I bond and formation of the spirocyclic arsenic(v) compound (90). The six-co-ordinate arsenic(v) anions (91) were produced by addition of an alcohol or phenol to an arsolan in the presence of triethylamine, the latter abstracting a proton and forming the required cation. ... 

Scheme 18. Statistical route to unsymmet-rically substituted derivatives of tripheny-lene. Reagents (a) electrochemical, FeCl, or chloranil oxidation.

Porphyrin Synthesis. Afeso-tetraalkylporphyrins are formed in good yields ftom condensation of aliphatic aldehydes with pyrrole thermally activated KIO catalyzes the polymerization-cyclization to porphyrinogen, followed by p-Chloranil oxidation (eq 11). ... 

Because Pd(II) salts, like Hgtll) salts, can effect electrophilic metallation of the indole ring at C3, it is also possible to carry out vinylation on indoles without 3-substituents. These reactions usually require the use of an equiv. of the Pd(ll) salt and also a Cu(If) or Ag(I) salt to effect reoxidation of the Pd. As in the standard Heck conditions, an EW substitution on the indole nitrogen is usually necessary. Entry 8 of Table 11.3 is an interesting example. The oxidative vinylation was achieved in 87% yield by using one equiv. of PdfOAcfj and one equiv. of chloranil as a co-oxidant. This example is also noteworthy in that the 4-broino substituent was unreactive under these conditions. Part B of Table 11.3 lists some other representative procedures. 

Chlormadinone (38) is prepared from hydroxyprogesterone (39) by epoxidation and treatment of the epoxide with hydrochloric acid to provide the chloroalkene (40). Oxidation, ie, dehydrogenation, with chloranil, provides chlormadinone (38), which may be acetylated to provide chlormadinone acetate (63,64). 

Derivatives of ubiquiaones are antioxidants for foodstuffs and vitamins (qv) (217,218). Ubichromenol phosphates show antiinflammatory activity (219). Chroman o1 compounds inhibit oxidation of fats and can be used ia treatment of macrocytic anemias (220). Monosulfate salts of 2,3-dimethoxy-5-methyl-6-substitutedhydroquiaone have been reported to be inhibitors of Hpid oxidation ia rats (221). Polymers based on chloranilic and bromanilic acid have been prepared and contain oxygenated quiaones (63), which are derived from 1,2,3,4-benzenetetrol (222). 

Dioxopiperazines are amongst the most ubiquitous of natural products (75FOR(32)57) and they are formally derived by the cyclodimerization of a-amino acids (69CCC4000) or their esters. A number of methods are available for their oxidation to the corresponding pyrazines. Treatment of 2,5-dioxopiperazines with triethyl- or trimethyl-oxonium fluorobor-ate followed by oxidation with DDQ, chloranil or iodine results in pyrazine formation, usually in high yields (Scheme 63) (72JCS(P1)2494). 

Again, as with pyridopyrimidines, the main reaction is oxidation of di- or poly-hydro derivatives to fully aromatic structures, often merely by air or oxygen. In some cases the reagent of choice is mercury(II) oxide, whilst other reagents used include sulfur, bromine, chloranil, chromium trioxide-acetic acid, hydrogen peroxide, and potassium ferricyanide, which also caused oxidative removal of a benzyl group in the transformation (306) (307)... 

Isoxazole compounds can be converted into the corresponding isothiazoles by successive catalytic hydrogenation, sulfuration with phosphorus pentasulfide and oxidation with chloranil (72AHC(14)l, 75SST(3)541). 2,1-Benzisoxazoles give the 2,1-benzisothiazoles directly, by the action of phosphorus pentasulfide in either pyridine or molten imidazole (73SST(2)556, 77SST(4)339). (See also Chapter 4.16 for further discussion of these topics.)... 

In extension of this work, Sugasawa and Yoshikawa have shown that d/- omolaudanosoline (XIII), on oxidation by chloranil in presence of acetic acid, also gives rise to a dehydro-product, which on methylation furnishes 2 3 11 12-tetramethoxy-8-methyl-6 7 15 16-tetrahydro-5 18 9 14-dibenzopyridocolinium salts (XIV). 

An explanation for the difference in behavior of chloranil and DDQ towards A -3-ketones was first provided by Ringold and Turner. The A -enol (67) is produced faster than the more stable A -enol (68) but is not attacked appreciably by chloranil, which lacks sufficient oxidizing potential. Instead, the more easily oxidized A -enol (68) is dehydrogenated to (69) as it is produced. With DDQ, the faster formed A -enol (67) can be effectively dehydrogenated and the A -3-ketone (70) is formed ... 

The oxidation of organic compounds by manganese dioxide has recently been reviewed. It is of limited application for the introduction of double bonds, but the advantages of mildness and simple workup make it attractive for some laboratory-scale transformations. Manganese dioxide is similar to chloranil in that it will oxidize A -3-ketones to A -dienones in refluxing benzene. Unfortunately, this reaction does not normally go to completion, and the separation of product from starting material is difficult. However, Sondheimer found that A -3-alcohols are converted into A -3-ketones, and in this instance separation is easier, but conversions are only 30%. (cf. Harrison s report that manganese dioxide in DMF or pyridine at room temperature very slowly converts A -3-alcohols to A -3-ketones.)... 

The immediate outcome of the Hantzsch synthesis is the dihydropyridine which requires a subsequent oxidation step to generate the pyridine core. Classically, this has been accomplished with nitric acid. Alternative reagents include oxygen, sodium nitrite, ferric nitrate/cupric nitrate, bromine/sodium acetate, chromium trioxide, sulfur, potassium permanganate, chloranil, DDQ, Pd/C and DBU. More recently, ceric ammonium nitrate (CAN) has been found to be an efficient reagent to carry out this transformation. When 100 was treated with 2 equivalents of CAN in aqueous acetone, the reaction to 101 was complete in 10 minutes at room temperature and in excellent yield. 

Tile same methodology as mentioned for the preparation of (9) was applied for the synthesis of 8-nitro-l,6-naphthyridines. Heating diethyl N- 3-nitropyridin-4-yl)aminomethylenemalonate (12) in diphenyl ether yields ethyl 8-nitro-l,6-naphthyridin-4(lH)-one 3-carboxylate (13) (63JCS4237, 30%) and acid treatment of 4-( y, y-diethoxypropylamino)-5-nitro-2-(/3,/3 -trifluoroethoxy)-pyridine (14) gives in a similar way 8-nitro-5-(/3, /3-triflu-oroethoxy)-l,2-dihydro-l,6-naphthyridine (15, 76%). Subsequent oxidation with chloranil, acid hydrolysis, and methylation with methyl iodide gives 8-nitro-6-methyl-l,6-naphthyridin-5(6H)-one (16,63%) (81JHC941). 

The ease with which the dipolarophile interacts with vinylacetylenes depends mainly on a spatial factor. The study of the reactions of alkylthiobuten-3-ynones-l and their selenic and telluric analogs with DPNT shows that, in this case, nitrilimine also acts as a nucleophilic agent with a nucleophilic center on the carbon atom of the 1,3-dipole and always adds to the terminal carbon of the enyne system to form l,3-diphenyl-5-/ -2-pyrazolenines. The oxidation of the latter with chloranil leads to alkynylpyrazoles (65ZOR51). 

The much simpler steroid, 253, was fortuitously found to fulfill this role when injected into animals. Its lack of oral activity was overcome by incorporation of the 7a-thioacetate group. Reaction of the ethisterone intermediate, 77b, with a large excess of an organomagnesium halide leads to the corresponding acetylide salt carbonation with CO2 affords the carboxyllic acid, 251. This is then hydrogenated and the hydroxy acid cy-clized to the spirolactone. Oppenauer oxidation followed by treatment with chloranil affords the 4,6-dehydro-3-ketone (254). Conjugate addition of thiolacetic acid completes the synthesis of spironolactone (255), an orally active aldosterone antagonist. ... 

Tricarbonyl[t/M-(ethoxycarbonyl)-l//-azepine]iron(0) (30) with the 2-oxyallyl cation derived from 2,4-dibromo-2,4-dimethylpentan-3-one and nonacarbonyldiiron(O) yields a mixture of adducts which, after oxidative decomplexation with tetrachloro-l,2-benzoquinone (o-chloranil), affords the tetrahydrofuro[2,3-A)azcpine derivative 33 and the 3-substituted 1H-azepine-l-carboxylate 34.227... 

Treatment of l-ethylideneamino-3-methylindole 95 with p-toluene sulfonic acid in boiling benzene gave l,2-dihydro[l,2,4]triazino[l,6-a]indole 96 (75CPB2891). The reaction was said to be due to an initial formation of a Diels-Alder-type adduct followed by the liberation of 3-methylindole. Compound % was oxidized either on exposure to air or by the action of chloranil to give 97 (Scheme 24). 

In the case of tertiary N-ethylamine derivatives the N-ethyl group is first selectively oxidized by p-chloranil to an enamino group which then condenses with excess p-chloranil to a blue aminovinylquinone derivative [7]. Secondary N-ethyl derivatives do not yield blue aminovinylquinone derivatives they probably react directly with chloranil by nucleophihc attack at one of the four chlorine atoms to yield aminoquinones of other colors [7], It has also been suggested that some classes of substances react to yield charge transfer complexes [1, 5, 8, 12],... 

Pd2(dba)3/l,4-bis(diphenylphosphino)butane (DPPB) in the presence of 2-mercaptobenzoic acid <95TL1267>. The Af-allylindolines can be easily oxidized to the corresponding indoles at room temperature with o-chloranil. Additionally, Al-allylanilines were also found to undergo aromatic 3-aza-Cope rearrangements in the presence of Zeolite catalysts to give indoline derivatives as the major product <96TL5281>. 

The oxidation of N ADH has been mediated with chemically modified electrodes whose surface contains synthetic electron transfer mediators. The reduced form of the mediator is detected as it is recycled electrochemically. Systems based on quinones 173-175) dopamine chloranil 3-P-napthoyl-Nile Blue phenazine metho-sulphatemeldola blue and similar phenoxazineshave been described. Conducting salt electrodes consisting of the radical salt of 7,7,8,8-trtra-cyanoquinodimethane and the N-methylphenazium ion have been reported to show catalytic effects The main drawback to this approach is the limited stability... 

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