Methoxyphenol groups

The voltammetric response of curcumin and carthamin must, in principle, be dominated by the oxidation of the phenol and/or methoxyphenol groups (see Scheme 2.2). The electrochemistry of methoxyphenols has claimed considerable attention because of their applications in organic synthesis [159-163]. As studied by Quideau et al., in aprotic media, 2-methoxyphenols are oxidized in two successive steps into cyclohexadienone derivatives [163], whereas a-(2)- and a-(4-methoxyphenoxy) alkanoic acids undergo electrochemically induced spirolac-tonization to develop synthetically useful orthoquinone bis- and monoketals. In the presence of methanol, the electrochemical pathway involves an initial one-electron loss, followed by proton loss, to form a monoketal radical. This undergoes a subsequent electron and proton loss coupled with the addition of alcohol to form an orthoquinone monoketal. The formal electrode potential for the second electron transfer... 

Taken together these experiments establish a) the formation of the berberine bridge by oxidative cyclization of the iV-methyl group, (6) the derivation of the methylenedioxy group by oxidative cyclization of the 0-methoxyphenol grouping, and (c) the validity of laudanosoline and reticuline as intermediates in the biosynthetic pathway. 

Fig. 1. A single step perturbation fails for the mutation of p-methylphenol to p-methoxyphenol because no configuration with a cavity large enough to accommodate the methoxy group is sampled in a simulation of p-methylphenol in water.

When camphene reacts with guaiacol (2-methoxyphenol), a mixture of terpenyl phenols is formed. Hydrogenation of the mixture results ia hydrogenolysis of the methoxy group and gives a complex mixture of terpenyl cyclohexanols (eg, 3-(2-isocamphyl) cyclohexanol [70955-71 (45)), which... 

In the first synthesis of T, the diphenyl ether was formed from -methoxyphenol and 3,4,5-triiodonitrobenzene. The nitro group was replaced by a nitril which was then built up into the alanyl side chain by a series of steps (10). 

A novel application of a phenyl aryldiazosulfone was found by Kessler et al. (1990). l-[4-(7V-Chlorocarbonyl-7V-methylamino)phenyl]-2-(phenylsulfonyl)diazene (6.18) is an acid chloride with a potential diazonio group. The above authors showed that in organic solvents (THF, etc.) this compound reacts easily, as expected, with nucleophiles (HNu), e.g., with aliphatic, aromatic, or heterocyclic amines, with cystine dimethyl ester, or with 4-methoxyphenol at the carbonyl function, yielding... 

Table 12-2 gives some of Sterba s results for 1-naphthol, resorcinol, 1-methoxy-naphthalene, 3-methoxyphenol and 1,3-dimethoxybenzene. The data in the table show that the 1-naphthoxide ion is 108 times more reactive than the undissociated naphthol, which is 102 times more reactive than 1-methoxynaphthalene. The rate ratios for the monoanion of resorcinol relative to resorcinol, 3-methoxyphenol, and 1,3-dimethoxybenzene are of similar magnitudes. The dissociation of both OH groups of resorcinol gives rise to a rate constant (2.83 X 109 m -1 s-1) which, in our opinion, is probably mixing- or diffusion-controlled (see Sec. 12.9). 

Eugenol, 4 allyl-2-methoxy phenol, is capable of forming cements with ZnO, CuO, MgO, CaO, CdO, PbO and HgO (Brauer, White Moshonas, 1958 Nielsen, 1963). Other 2-methoxy phenols are also capable of forming cements with metal oxides, provided the allyl group is not in a 3- or 6-position where it sterically hinders the reaction (Brauer, Argentar Durany, 1964). These include guaiacol, 2-methoxyphenol, and the allyl and propylene 2-methoxy phenols. 

Pesticides containing methyl or other alkyl substituents maybe linked to N or 0 (i.e., N- or O-alkyl substitution). An N- or O-dealkylation catalyzed by microorganisms frequently results in loss of the pesticide activity. Phenylurea (see Chap. 1) becomes less active when microorganisms AT-demethylate the molecules (e. g., the conversion of Diuron to the normethyl derivative, Fig. 7). The subsequent removal of the second AT-methyl group renders the molecule fully nontoxic [169]. On the other hand, the microbial O-demethylation of Chloroneb creates the non-toxic product 2,5-dichloro-4-methoxyphenol (Fig. 7). 

Instead of 3-amlno-l-group would be on the xyethvl)acrylamide, t -15 C Instead of -5 to erature (9 ) to obtain a action, the mixture was iltered. The filtered Ide salt was washed several lie. The filtrates were nitrile was removed by amounts of p-methoxyphenol... 

When the reaction is run with /tara-methoxyphenol up to 44% of photoproducts correspond to substitution of the methoxy group by tert-bvXyl and acetyl (Scheme 17). This is in agreement with the observation that photolysis of 4-methoxyphenyl acetate yields, among other products, para-acetyl phenol [32]. 

Ishihara, Yamamoto, and coworkers demonstrated that 26 SnCl4 is an artificial cyclase that is useful for not only achiral but also chiral substrates. The diastereo-selective cyclization of ( )-nerolidol (29) has been examined with 1 equiv of the achiral LBA, 2-methoxyphenol (32) SnCl4, in dichloromethane at —78°C (entry 1, Table 12.1). Cyclization of ( )-29 bearing an acid-sensitive allylic hydroxy group gives a complex reaction mixture, and the desired trans-fused 2-oxabicyclo[4.4.0]... 

With 4-methoxyphenols, the phenoxyl formed is further stabilized by delocalization of the unpaired electron to the p-type orbital of the methoxyl oxygen (105 -106). This interaction is allowed in vitamin E and in compound 103 but prohibited in compound 104 because the former two compounds exist in conformation 107 and the latter in conformation 108. In conformation 108, due to the methyl groups in ortho position, the methoxyl group is twisted out of the plane of the aromatic ring and the delocalization of the methoxyl oxygen electron pair is consequently prohibited. 

Hammett s equation was also established for substituted phenols from the elementary hydroxyl radical rate constants. The Hammett resonance constant was used to derive a QSAR model for substituted phenols. The simple Hammett equation has been shown to fail in the presence of electron-withdrawing or electron-donating substituents, such as an -OH group (Hansch and Leo, 1995). For this reason, the derived resonance constants such as o°, cr, and o+ were tested in different cases. In the case of multiple substituents, the resonance constants were summed. Figure 5.24 demonstrates a Hammett correlation for substituted phenols. The least-substituted compound, phenol, was used as a reference compound. Figure 5.24 shows the effects of different substituents on the degradation rates of phenols. Nitrophenol reacted the fastest, while methoxyphenol and hydroxyphenol reacted at a slower rate. This Hammett correlation can be used to predict degradation rate constants for compounds similar in structure. 

Based on these results, 2,6-di-/L rr-butyl-4-methylphenol (BHT) and 3-terf-butyl-4-methoxyphenol (BHA), bearing a phenolic hydroxy group, have been used in recent times as anti-oxidants in many kinds of foods. 

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