Pyridines 3.4- dihydroxy

Anthralin [1143-38-0] is acetylated using acetyl chloride in toluene and a pyridine catalyst to furnish 1,8-dihydroxy-lO-acetylanthrone [3022-61-5], an intermediate in the preparation of medications used in treating skin disorders, such as warts, psoriasis, and acne (38). Sugar esters can be similarly prepared from acetyl chloride under anhydrous conditions (39). 

Ethers of benzenepentol have been obtained by Dakin oxidation of the appropriately substituted acetophenone. Thus, the oxidation of 2-hydroxy-3,4,6-ttimethoxyacetophenone and 2-hydroxy-3,4,5-ttimethoxyacetophenone with hydrogen peroxide ia the presence of alkali gives l,2-dihydroxy-3,4,6-ttimethoxybenzene and l,2-dihydroxy-3,4,5-ttimethoxybenzene, respectively further methylation of these ethers yields the pentamethyl ether of benzenepentol (mp 58—59 degC) (253). The one-step aromatization of myoinositol to produce esters of pentahydroxybenzene is achieved by treatment with carboxylic acid anhydrides ia DMSO and ia the presence of pyridine (254) (see Vitamins). 6-Alkyl- or... 

A more recent development in quinone chemistry has been the tandem reaction sequence. In seeking elegant syntheses of complex molecules, careful orchestration of transformations has become essential. The use of the Thiele-Winter reaction in tandem with arylation gives good yields of pharmacologically interesting heterocycles, such as (62), from 2,5-dihydroxy-l,4-ben2oquinone [615-94-1] and pyridines, where R = H or CH (60). 

A third synthesis which has resulted in the preparation of rieinine and a number of its derivatives is due to Schroeter, Seidler, Sulzbacher and Kanitz,i2 who foimd that cyanoacetyl chloride polymerises spontaneously to 6-chloro-2 4-dihydroxy-3-cyano-pyridine. The di-sodium derivative of this with methyl sulphate produces A -methyl-6-chloro-4-hydroxy-3-cyano-2-pyridone (6-chlororicininic acid), the mono-sodium derivative of which, with methyl bromide or sulphate, is converted into 6-chlororicinine and the latter is reduced by zinc and sulphuric acid to rieinine. A fourth synthesis, starting from 3-nitro-4-pyridone, is due to Reitmann. ... 

Acetonides are quite stable to base, and to oxidation, dehydration and acylation reactions carried out in pyridine. They are cleaved by acid hydrolysis. The 17,21-acetonides of 17a,21-dihydroxy-20-keto steroids and related acetals are split by very mild acid conditions. ... 

On the basis of its reaction with diazomethane, 2,4-dihydroxyquino-line was reported to exist as 4-hydroxyquinol-2-one in the solid state and as an equilibrium mixture of this form with 2-hydroxyquinol-4-one in solution. Using the infrared criteria for o- and p-quinonoid forms (see Section II,L), the spectra of 2,4-dihydroxy-pyridine and -quinoline indicated that both quinonoid forms, e.g., 12 (Z = NH) and 13 (Z — NH), were present and that the nonaroraatic form (43) was absent. ... 

Demethylation of trequinsin (3) with a 65 35 mixture of AcOH and 48% HBr at 115 °C for 3 h gave mainly 10-hydroxyl derivatives 148 (R = r = H), which was accompanied by traces of its 9-hydroxyl and 9,10-dihydroxy derivatives. In boiling 48% HBr for 2 h its 9,10-dihydroxy derivative formed in 63% yield (98IJC(B)1). 9-Methoxy group of 3 and that of its 2-[(2,6-dimethyl-4-carboxyphenyl)imino] derivative 178 (R = COOH) was selectively demethylated by the treatment with 60% NaOH and EtSH in HMPA. Treatment of 3 with pyridine HCl in boiling pyridine for 20 min afforded its 9,10-dihydroxy-3-desmethyl derivative in 65% yield. 4 -Hydroxymethyl... 

Preparation of 9, 11 -Epoxy-17a-21 -Dihydroxy-16 -Methyl-4-Pregnene-3 0-Dione 21-Acetate To a stirred solution of 100 mg of the 9a-bromo-11(3,17a,2Ttrihydroxy-16 3-methyl-4-pregnene-3,20-dione 21-acetate in 3 ml of tetrahydrofuran and 1 ml of methanol under nitrogen was added 1.02 ml of 0.215 N methanolic sodium methoxide. After 10 minutes at 25°C, 0.2 ml of acetic acid was added and the methanol removed in vacuo. The residue was acetylated with 1.00 ml of pyridine and 0.5 ml of acetic anhydride at 60°C for 70 minutes. The mixture was taken to dryness in vacuo, water added, and the product extracted into chloroform. The residue was crystallized from ether-acetone to give pure 9(3,11 (3-epoxy-17a,21-dihydroxy-16(3-methyl-4-pregnene-3,20-dione 21-acetate. 

A solution of 1.0 g of A -3,11-diketo-20-cyano-21-acetoxy-pregnene in 10 cc of benzene is treated with 1.0 g of osmium tetroxide and 0.43 g of pyridine. After standing at room temperature for 18 hours, the resulting solution is treated successively with 50 cc of alcohol, and with 50 cc of water containing 2.5 g of sodium sulfite. The mixture is stirred for 30 hours, filtered, and the filtrate acidified with 0.5 cc of acetic acid and concentrated to small volume in vacuo. The aqueous suspension is then extracted four times with chloroform, the chloroform extracts are combined, washed with water and concentrated to dryness in vacuo. Recrystallization of the residue from acetone gives 3,11,20-triketo-17(a)-21-dihydroxy-pregnane MP 227° to 229°C. This compound is then treated with acetic anhydride and pyridine for 15 minutes at room temperature to produce 3,11,20-triketo-17(a)-hydroxy-21-acetoxy-pregnane or cortisone acetate. 

C Preparation of p,p -Diacetoxybemhydrylidenecyclohexane 56 g of p,p -dihydroxy-benzhydrylidenecyclohexane (0.2 mol) was mixed with 250 ml of acetic anhydride and 500 ml of pyridine. The mixture was refluxed for 2 hours and was then poured into water, the substance crystallizing out. The crystals were filtered off and washed with water. Finally the substance was recrystallized from ethanol. Yield 62 g. MP 135° to 136°C. 

Both 2-hydroxy- and 3-hydroxypyridine are hydroxylated to 2,5-dihydroxypyridine by strains of Achromobacter sp. (Houghton and Cain 1972). These metabolites are probably, however, formed by different reactions whereas 3-hydroxypyridine behaves as a true pyridine, addition of H2O across the Cg Nj bond would produce the 2,5-dihydroxy compound 2-hydroxypyridine is a cyclic amide and hydroxylation apparently occurs at the diagonal position. The degradation of 4-hydroxypyridine is also initiated by hydroxylation and is followed by dioxygenation before ring fission (Figure 10.12) (Watson et al. 1974). 

Scheme 4. The compounds and intermediates on the rear plane of the bicubic system (farthest from the reader) are protonated on the pyridine nitrogen atom those on the front plane (nearest the reader) are not. Laviron s work has shown that the reduction of 14 and its corresponding N-oxide34, and indeed probably most aryl nitro compounds, proceeds by an ECEC sequence leading to the neutral N,N-dihydroxy [ArN(OH)2] intermediate at all proton concentrations from Ho = —6 to pH 9.6. This substance then loses water to form the nitroso compound, which then undergoes a second sequence leading to the arylhydroxylamine.

Dihydroxy-l,2-dihydropyridine, see Pyridine cis-2,3-Dihydroxy-2,3-dihydrotoluene, see Toluene 2,2 -Dihydroxy-4,4 -dimethylbiphenyl, see 4-... 

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