Hydroxy- and methoxy-substituted

Trimethylsilyl derivatives of ten hydroxy- and methoxyhydroxyflavonoids have been studied by the GC-FTIR technique." " The correlation found between retention and gas-phase IR data was used in structural identification of compounds having very similar chromatographic behavior. The shift of the carbonyl frequency gave information on the presence of substitution. Some hydroxy- and methoxy-substituted flavones have been studied following carbon dioxide supercritical fluid chromatography on polymethylsiloxane capillary columns using flame ionization and FTIR detection." " " ... 

In practice, extrapolations of p fR in water have usually used the older acidity function based method, for example, for trityl,61,62 benzhydryl,63 or cyclopropenyl (6) cations.66,67 These older data include studies of protonation of aromatic molecules, such as pKSi = —1.70 for the azulenium ion 3,59 and Kresge s extensive measurements of the protonation of hydroxy- and methoxy-substituted benzenes.68 Some of these data have been replotted as p fR or pKa against XQ with only minor changes in values.25,52 However, for more unstable carbocations such as 2,4,6-trimethylbenzyl, there is a long extrapolation from concentrated acid solutions to water and the discrepancy is greater use of an acidity function in this case gives pA 2° = —17.5,61 compared with —16.3 (and m = 1.8) based on X0. Indeed because of limitations to the acidity of concentrated solutions of perchloric or sulfuric acid pICs of more weakly nucleophilic carbocations are not accessible from equilibrium measurements in these media. 

Comparisons of structurally related hydroxy- and methoxy-substituted cations show that hydroxy is more stabilizing by between 4 and 5 log units. This difference was recognized 20 years ago by Toullec who compared pifas for protonation of the enol of acetophenone and its methyl ether145 (-4.6 and 1.3, respectively) based on a cycle similar to that of Scheme 15, but with the enol replacing the hydrate, and a further cycle relating the enol ether to a corresponding dimethyl acetal and methoxycarbocation.146 Toullec concluded, understandably but incorrectly, that there was an error in the pA a of the ketone (over which there had been controversy at the time).147,148 In a related study, Amyes and Jencks noted a difference of 105-fold in reactivity in the nucleophilic reaction with water of protonated and O-methylated acetone and concluded that the protonated acetone lacked a full covalent bond to... 

The old Maquenne synthesis of imidazoles [64] is seldom used nowadays. It was originally used to make imidazole-4,5-dicarboxylic acids from tartaric acid dinitrate and either an aliphatic aldehyde or formaldehyde precursor in the presence of ammonium ions at pH 3.5-6.5. The procedure is not an entirely pleasant experience, and has been happily superseded by other approaches, but it may be useful on occasion to make compounds such as vinyl-, hydroxy-and methoxy-substituted 2-arylimidazole-4,5-dicarboxylic acids [65]. Use of dialkyltartrate dinitrates gives the corresponding imidazole-4,5-dicarboxylates in 45-65% yields [31]. 

Lignin. Lignin is a phenolic substance consisting of an irregular array of variously bonded hydroxy- and methoxy-substituted phe-nylpropane units. The precursors of lignin biosynthesis are p-cou-maryl alcohol (I), coniferyl alcohol (II), and sinapyl alcohol (III). I... 

Papageorgiou, C., Petcher, T.J., and Waldvogel, E., Synthesis of hydroxy- and methoxy-substituted octahydrobenzo[g]isoquinolines as potential ligands for serotonin receptors, Helv. Chim. Acta, 72, 1463, 1989. 

Isoxazoles are initially metallated in the 5-position. The 5-stannyl derivatives 102 (Scheme 43) could be cross-coupled with hydroxy- and methoxy-substituted 2-iodophenols... 

Lignin is an amorphous, cross-linked polymer network consisting of an irregular array of variously bonded hydroxy- and methoxy-substituted phenylpropane units [13]. The chemical structure varies depending on its source. Lignin is less polar than cellulose and acts as a chemical adhesive within and between fibers. 

There is a wide diversity of chemical structures of anthraquinone colorants. Many anthraquinone dyes are found in nature, perhaps the best known being alizarin, 1,2-dihydroxyanthraquinone, the principal constituent of madder (see Chapter 1). These natural anthraquinone dyes are no longer of significant commercial importance. Many of the current commercial range of synthetic anthraquinone dyes are simply substituted derivatives of the anthraquinone system. For example, a number of the most important red and blue disperse dyes for application to polyester fibres are simple non-ionic anthraquinone molecules, containing substituents such as amino, hydroxy and methoxy, and a number of sul-fonated derivatives are commonly used as acid dyes for wool. 

The present homoallylation with siloxy- and methoxy-substituted dienes may be of great synthetic use. The product 42 is easily converted to anti-5-phenyl-5-hydroxy-3-methylpentanal (Scheme 9) hence the diene 41f may be regarded as a synthetic equivalent of a bis-homoenolate of 3-methylbutanal, being capable of introducing 1,3-anti relationship between the methyl and hydroxy groups in the product. 

Lignin is a polymer built up of phenylpropane units substituted with hydroxy and methoxy groups, see Figure 48. Lignin is a three-dimensional molecule like a 3-D matrix, see Figure 48 [65]. 

For phenol one can compare the effects of hydroxy and methoxy substituents. Scheme 19 shows effects of O-methyl substitution on pATas for protonation of a benzene ring containing one, two, and three hydroxy substituents. The pK s for di- and trihydroxy-substituted and methoxy-substituted benzenes were measured directly by Kresge et al.68 Again the stabilities of the hydroxy-substituted cations in water are consistently greater than methoxy. The importance of solvation in controlling these effects is demonstrated by the inversion of relative pK s of trihydroxy and trimethoxy benzene in concentrated solutions of perchloric acid.68 Thus the difference in p/fas is matched by a... 

These three compounds differ from each other in the substitution pattern of the B-ring apimaysin has one hydroxyl group on the 4 position of the firing, maysin has a 3, 4 -dihydroxy substitution pattern, and methoxymaysin has a 4 -hydroxy, 3 -methoxy substitution pattern. These compounds accumulate in the silks of maize (i.e. the styles attached to the ovules) and are thought to act in a manner similar to chlorogenic acid (see Figure 6-1) when insects damage the silks. 

Recently Liu and coworkers used (porphyrin)iron(III) chloride complex 96 to promote 1,5-hydrogen transfer/SHi reactions of aryl azides 95, which provided indolines or tetrahydroquinolines 97 in 72-82% yield (Fig. 24) [148]. The reaction starts probably with the formation of iron nitrenoids 95A from 95. These diradicaloids undergo a 1,5- or 1,6-hydrogen transfer from the benzylic position of the ortho-side chain. The resulting benzylic radicals 95B react subsequently with the iron(IV) amide unit in an Sni reaction, which liberates the products 97 and regenerates the catalyst. /V,/V-Dialkyl-w// o-azidobenzamides reacted similarly in 63-83% yield. For hydroxy- or methoxy-substituted indolines 97 (R2=OH or OMe) elimination of water or methanol occurred from the initial products 97 under the reaction conditions giving indoles 98 in 74—78% yield. 

In the photosynthetic bacteria Rhodomicrobium vannielii, which normally contains acyclic carotenoids with tertiary hydroxy- and methoxy-groups at C-1 and C-T, phytoene only accumulated when diphenylamine was present, but the occurrence of hydroxy-derivatives of phytofluene, 7,8,11,12-tetrahydrolycopene, neurosporene, and lycopene in the presence of the inhibitor indicated that hydroxylation could take place at any level of desaturation although only the more desaturated half of the molecule was so substituted. 

A series of substituted salicylaldimines 54 was prepared by the condensation of various hydroxy and methoxy salicylaldehydes and 2,6-di-terr-butyl-4-aminophenol. It was shown by UV-Vis and H NMR spectroscopy investigations that compounds 54 exist in solutions both in the phenol-imine and keto-enamine tautomeric forms. ... 

Various reactions involving the hydroxy and methoxy groups have been performed. Trimethylsilylation of pyridazinones was studied, and were synthesized phosphorothioates and heteroaryloxypyridazines. N-Acetyl maleic hydrazide is not obtained by the previously described procedure. However, with ketene an 0,N-diacetyl derivative is formed that in hot ethanol gives the stable O-acetyl maleic hydrazide. Maleic hydrazide reacts to give with diarylnitrilimines O-substitution products and with sulfonyl chlorides the corresponding O-sulfonyl derivatives, ... 

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