Aryl Hydroxy Groups

Aryl hydroxy groups have been removed by first converting them into an ether by reaction with a heterocycle such as l-phenyl-5-chlorotetrazole (61) and then hydrogenolyzing the ether with platinum or palladium (Eqn. 20.42).97-99 other aryl ether groups that are readily hydrogenolyzed to give the benzene are the benzoxazole, 62, sulfonates, 63, and phosphates, 64.  

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Aryl, heteroaryl, and alkenyl cyanides are prepared by the reaction of halides[656-658] or triflates[659,660] with KCN or LiCN in DMF, HMPA, and THF. Addition of crown ethers[661] and alumina[662] promotes efficient aryl and alkenyl cyanation. lodobenzene is converted into benzonitrile (794) by the reaction of trimethylsiiyl cyanide in EtiN as a solvent. No reaction takes place with aryl bromides and chlorides[663]. The reaction was employed in an estradiol synthesis. The 3-hydroxy group in 796 was derived from the iodide 795 by converting it into a cyano group[664]. 

A large number of variously 2-, 4-, and 5-substituted thiazoles with alkyl, aryl, hydroxy, methylthio, mercapto, halo, and nitro groups have been analyzed by thin-layer chromatography on silica and alumina by the Stahl s technique (167, 170, 172). Among the many systems recommended for the elution of these compounds are the following ... 

The respective amide was prepared from 7-substituted 5-oxo-2,3-dihydro-5//-pyrido[l,2,3-de]-l,4-benzoxazine-6-carboxylic acids via acid chlorides with different benzylamines (00M1P3). 6-Carboxamides were N-benzylated, and a side-chain phenolic hydroxy group was O-alkylated. 7-Aryl-5-oxo-2,3-dihydro-5//-pyrido[l, 2,3-r/e]-1,4-benzoxazine-6-carboxylic acid was obtained from the ethyl ester by alkalic hydrolysis. 

Hydroxy group of rru -7,9u-H-7-(prepared from 7-formyl-2-(2-pyrimidyl)perhydropyrido[l,2-u]pyrazine by the treatment with MeOCH2P(Ph)3Cl in the presence of -Pr2NH in THF at 0°C, than with BuLi at room temperature (99MIP6). 

Aldehydes and ketones are similar in their response to hydrogenation catalysis, and an ordering of catalyst activities usually applies to both functions. But the difference between aliphatic and aromatic carbonyls is marked, and preferred catalysts differ. In hydrogenation of aliphatic carbonyls, hydrogenolysis seldom occurs, unless special structural features are present, but with aryl carbonyls either reduction to the alcohol or loss of the hydroxy group can be achieved at will. 

Hydroxy groups on benzene rings can be replaced by NH2 groups if they are first converted to aryl diethyl phosphates. Treatment of these with KNH2 and potassium... 

The importance of protonated N-hydroxy arylamines as ultimate carcinogens has been suggested for some time (28,40,139). From studies on their reactivity with nucleic acids at different pH s (2,15,16,63,130,131), the pK for protonation of the N-hydroxy group appears to be between pH 5a and 6 thus, a significant proportion (1-10%) of the N-hydroxy derivative exists as the protonated form even under neutral conditions. This would account for the significant levels of covalent modification of DNA observed in vitro by reaction with N-hydroxy arylamines at neutral pH. Consequently, it has been proposed that in vivo formation of non-acetylated aryl... 

The aggregation behaviour and tautomerism of three 0,0 -dihydroxy and one o-hydroxy-o -methoxy monoazo dyes have been studied by UV-visible spectroscopy [17]. Evidence of monomer-dimer equilibria was obtained for all four of these mordant dye structures. Intermolecular hydrogen bonding between the hydroxy groups and hydrophobic interaction between aryl nuclei contribute to the dimerisation effect. 

Substituents with lone electron pairs, such as alkoxy, hydroxy, alkyl, and aryl-amino groups, are known as electron donors. The CH3 group, despite the absence of such free electron pairs, is also considered an electron donor. Functional groups with conjugated rr-electron systems, such as NOz, COOH, COOR, SOz, or SOzAr act as electron acceptors. 

Arene(alkoxy)carbene chromium complexes react with aryl-, alkyl-, terminal, or internal alkynes in ethers or acetonitrile to yield 4-alkoxy-1-naphthols, with the sterically more demanding substituent of the alkyne (Rl Figure 2.24) ortho to the hydroxy group. Acceptor-substituted alkynes can also be used in this reaction (Entry 4, Table 2.17) [331]. Donor-substituted alkynes can however lead to the formation of other products [191,192]. Also (diarylcarbene)pentacarbonyl chromium complexes can react with alkynes to yield phenols [332]. 

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