Naphthalenes, methoxylation

Other nucleophile-electrophile pairs for which the pm-disubstituted naphthalene system has been used to monitor potential bonding interactions are illustrated in [35] and [36], The methoxynitrile [35], for example, shows the same sort of evidence for a bonding interaction, marked by a 7° distortion from linearity at the nitrile carbon, in plane, and exactly away from the methoxyl oxygen (Procter et al., 1981) so also does the bipyridyl dinitrile [37] (Baxter et al., 1991). In the unique case of the 8-diazonium quinoline-N-oxide [36] the proximity of a formally negatively charged oxygen induces a distortion from linearity of 10.4° in the diazonium group (Wallis and Dunitz, 1984). 

The strength of the hydrogen bonds in the protonated amines can be increased by the use of larger and additional groups to provide further steric strain. For example, the difference in strain between l,8-bis(dimethylamino)-naphthalene [33] and 1,8-bis(diethylamino)naphthalene leads to a piC,-value for the ethyl derivative enhanced by 0.5 units (Hibbert, 1974), and a similar difference is also observed in the fluorene series for [41] and [42]. Further strain can be introduced into the naphthalene series by the use of 2- and 7-methoxyl groups as substituents. This is illustrated by the pA -values of 1,8-bis(dimethylamino)naphthalene [piC, = 12.1 (Hibbert, 1974)] and l,8-bis(di-methylamino)-2,7-dimethoxynaphthalene [p, = 16.1 (Hibbert and Simpson, 1987a)] and by the piC,-values of [35] pK = 7.49 (Hibbert and Hunte,... 

Substituent effects in addition of earbanions to 7r-arenechromium tricarbonyl complexes have been examined. Methyl and chloro substituents give mixtures of ortho- and mefa-substitution, with the amount of mem-isomer increasing with bulk of the anions. Methoxyl and dimethylamino substituents are strongly meta -directing. The more hindered 3-position of 1,2-dimethoxybenzene is substituted even by a tertiary carbanion. Naphthalene shows 99% a -substitution. A trimethylsilyi group is strongly para-directing. 

Important information relating to the chemical structure of different coals has been obtained by several investigators by means of the acid-catalyzed depolymerization method. Small quantities of pure compounds, such as methoxyl phenyl derivatives of benzofuran and xanthene as well as unresolved mixtures of derivatives of benzene, naphthalene, diphe-... 

When Nu is electron donating the product is as a rule more easily oxidized than the starting material, resulting in further oxidation under the reaction conditions and, frequently, complex reaction mixtures. The anodic methoxylation of naphthalene, which results in 1-methoxy-, 1,2-dimethoxy-, and 1,4-dimethoxynaphthalene, approximately in a 1 2 1 ratio, serves as an illustration of this problem [67]. However, in other cases, a single major product is obtained after a sequence of reactions, such as the oxidation of mesitylene in MeCN-diluted H2SO4 to 2,4,6-trimethyl-4-hydroxycyclohexa-2,5-dien-l-one in a substitution-elimination reaction [68] or the oxidation of anthracene in MeOH to 9,9,10,l0-tetramethoxy-9,10-dihydroanthracene in a substitution-addition reaction [Eq. (28)] [69]. 

Anodic methoxylation of aromatic ethers via the EEQCp mechanism has found its widest application in the synthesis of quinone bisketals (LXX) from para-dimethox-ybenzenes (LXIX) [79]. Yields are generally excellent, and the reaction is conveniently carried out at constant current in a single cell [42,80]. The reaction has also been shown to work well for naphthalenes [81] and benzothiophenes [82]. As shown in Table 4, a variety of substituents may be present on the ring. When substituents sensitive to cathodic reduction such as -CHO and -CH CHCO Me are present, a divided cell apparatus may be required to obtain reasonable yields of the corresponding bisketals. 

The anodic methoxylation of aromatic compounds such as naphthalene [41], anthracene [42], alkylbenzenes [31,43], phenols [44-46], anisoles [33,47-54] and other alkoxyben-zenes [53], methoxynaphthalenes [33], methoxyanthracenes [50,54], inden-l-ones [55], / a/r/-substituted anilides [56] and heterocyclic compounds, such as furans [57], thiophenes [58], and pyrroles [59], has received considerable attention. 

As discussed above, the absolute stereochemistry of halenaquinone (+)-l and halenaquinol (+)-2 has been theoretically determined by the calculation of the CD spectra of naphthalene-diene derivatives by means of the tt-electron SCF-CI-DV MO method. 18 To apply the same method to these xestoquinone compounds, xesto-quinol dimethyl ether (+)-74 was converted to naphthalene-diene derivative 75 by reduction with sodium borohydride in the presence of cerium(IIl) chloride23 and methanol, followed by treatment with pyridinium p-toluenesulfonate and methanol (Scheme 16).20 The product obtained was a mixture of two stereoisomers of the methoxyl group at the 4-position, from which a single isomer 75 was isolated as... 

In their seminal work published in 1999, Uang and co-workers demonstrated the potential of using inexpensive and stable oxovanadium(iv) complex VO(acac)2 to catalyze oxidative coupling reactions of 2-naphthols (Table 3.5). Molecular oxygen was identified as an efficient terminal oxidant. A bromo or methoxyl substituent was tolerated on the naphthalene ring (entries 2 and 3), but the reaction with the substrate bearing an ester... 

Scheme 15.9 is once again similar to Scheme 15.6 except that the protonation back reaction is bimolecular. Thus, the two-state formalism is applicable with some changes concerning the determination of the fourth unknown. Because the lifetime of N in the absence of reaction, tn = 1 / fn> cannot be reliably measured with N even at very low pH values, it has to be obtained with a parent compound, with which the proton transfer reaction does not occur (in this case, 2-methoxy-naphthalene). However, the implicit assumption of the procedure, that the lifetime measured with the methoxylated compound would be equal to tn, may be dangerous with the strongly hydrogen bonding solvent water (the most common solvent for proton transfer). 

Detailed analyses of the change in antifungal activity with chemical modification have appeared.3°>39 Naphthlomate-N is very active, but the other three naphthalene isomer combinations are inert. Various substituted phenols may be used in place of the p-naphthol moiety. Of the N-methyl (essential for activity) anilines tried, hydrogen, methyl, methoxyl, and halogen containing compounds were active whereas nltro, di-methylamino, carboxyl, etc., derivatives were inactive. The carbamates still retained some activity but other variations of the thiocarbamate system, such as the dithiocarbamate derivatives, were devoid of antifungal action. 

Mangion, D., Frizzle, M., Arnold, R.D., and Cameron, T.S., The photochemistry of acrylonitrile with methoxylated naphthalenes introducing the photochemical electrophile-olefin combination, aromatic substitution (Photo-EONAS) reaction. Synthesis, 8,1215, 2001. 

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