Derivatives of 1,4-Dihydroxybenzenes

Reactions of these compounds comprise those at the hydroxyl group and 

2-chloro-5-trifluoromethylpyridineindimethylformamidecontainingpotassiumfluoride on alumina by heating at 120°C for 9 hours afforded the corresponding ether in 88% yield. The 5-nitro analogue reacts similarly (ref. 170). 

Allyl or propargyl ethers of 4-methoxyphenol upon anodic oxidation directly gave quinone monoketals (ref.171). 

Substitution in the ring occurred when 4-methoxyphenol, glyoxylic acid and alumina were added to 2M sodium hydroxide and the mixture was stirred at ambient temperature for 12 hours giving a 75% yield of 2-hydroxy-5-methoxymandelic acid which upon oxidation gave 2-hydroxy-5-methoxybenzaldehyde (ref.173). 

Although the corresponding 4-methyl and 4-phenyl analogues failed to similarly react, 2-tert-butyl-4-methoxyphenol in acetic acid containing copper(ll) acetate when refluxed for 24 hours under argon afforded a 70% yield of 2-acetoxy-4-methoxy-6-tert-butylphenol (ref. 174). 

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Reaction with the electrophilic peroxodisulfate occurs preferentially at the para position, leading to formation of a cyclohexadienone derivative 5, which loses a proton to give the aromatic compound 6. Subsequent hydrolysis of the sulfate 6 yields 1,4-dihydroxybenzene 3 ... 

The main product of the Elbs reaction is the 1,4-dihydroxybenzene (hydro-quinone). If the para position is already occupied by a substituent, the reaction occurs at an ortho position, leading to a catechol derivative although the yields are not as good as for a hydroquinone. Better yields of catechols 7 can be obtained by a copper-catalyzed oxidation of phenols with molecular oxygen ... 

The two major routes to 3,4-dihydro-2JT-l,5-benzodioxepins (274) from (273) and (275) are applicable to a wide range of substituted derivatives. The 3-oxo derivative, important as a perfume odorant, can be prepared via the reaction of 1,2-dihydroxybenzene with chloroacetonitrile (75CJC2279) or via a Dieckmann cyclization (74USP3799892). 

It is well known that benzophenone generates a biradical through n-ir electronic transition under irradiation ( 340 nm). Irradiation of a mixture of 1,4-benzoquinone (34) and aromatic aldehydes in the presence of benzophenone generates 2-aroyl-l,4-dihydroxybenzene (35) [47-49]. This reaction comprises of the abstraction of a formyl hydrogen atom of an aromatic aldehyde by the oxygen-centered radical of the benzophenone biradical to form an aroyl radical and a 1,1-diphenylhydroxymethyl radical, and addition of the nucleophilic aroyl radical to 1,4-benzoquinone (34) to form a phenoxyl radical derivative, which finally abstracts a hydrogen atom from an aromatic... 

Another example of the effectiveness of the reaction O -coronaP] arene[3]tetrazines 54, a new class of macrocyclic compounds, were synthesized efficiently in a one-pot reaction via nucleophilic aromatic substitution of 3,6-dichlorotetrazine 53 with 1,4-dihydroxybenzene derivatives 55 in warm acetonitrile (14AGE13548). 

The antioxidant activity of phenol is also increased by the presence of additional hydroxyl group in the ortho or para positions. An example of such an antioxidant is TBHQ. The effectiveness of 1,2-dihydroxybenzene derivatives is attributed to a phenoxyl radical stabilised by an intramolecular hydrogen bond (11-8). The activity of 2-methoxyphenol is lower, because the generated radical cannot be stabihsed by a hydrogen bond. The antioxidant activity of 1,2-and 1,4-dihydroxybenzene is partly caused by the fact that the semi-quinone radical can be further oxidised to the corresponding o-quinone orp-quinone, respectively, by reaction with another lipid radical (Figure 11.7) or may disproportionate to the corresponding quinone and hydroquinone. 

Chapter 2 covers recent advances in the Synthesis of Quinoxalines involving the methods based on the (a) condensation of 1,2-diaminobenzenes and derivatives with various two-carbon unit suppliers, (b) condensation of o-benzoquinone diimines and diimides with various two-carbon unit suppliers, (c) condensation of A,A-dimethyl(dibenzyl)ethylenediamine with 1,2- and 1,4-dihydroxybenzenes, (d) synthesis of quinoxalines from aniline and its derivatives, (e) synthesis of quinoxalines from heterocyclic systems and (f) synthesis of quinoxalines based on the carbocyclic system. 

Chemically, NE is classified as a catecholamine. A catechol is a 1,2-dihydroxybenzene, and NE is a p-hydroxyethylaminodihydroxybenzene. Epinephrine is the N-methyl derivative of NE, and they both have acidic and basic functional groups. Physiologically, however, they behave as a base, being more than 90% protonated at pH 7.4 (pKa = 9.6) and functioning as an ionized acid. 

Inokuma et al have reported a further example of additions with crown ether derivatives. In this instance the additions are intermolecular and involve the dimerization of the vinylbenzene derivative (123) to afford the two adducts (124) and (125). The ion-complexing capabilities of the adducts were assessed. A layered ternary solid is formed between 1,2-dihydroxybenzene and trans- -(2-pyridyl)-2-(4-pyridyl)ethylene. Within this, the stilbene is held in a head-to-tail arrangement. Irradiation brings about the formation of a cyclobutane identified as (i )-c/ y,/ra y,/ra -l,3-bis(2-pyridyl)-2,4-bis(4-pyridyl)cyclobutane. An extension of this work to the use of 5-methoxyresorcinol as the template has demonstrated that quantitative yields of ladderanes (126) can be obtained by irradiation of the solid-state units represented as (127). The diazastilbene derivative (128) readily forms complexes with the tetra-acid (129). This acts as a supramolecular template and holds the ethene systems close enough for photochemical dimerization. ... 

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