1,6-Dimethoxynaphthalene

Acylation of 1,4-dimethoxynaphthalene with acetic anhydride (1.2 equiv) and aluminum chloride (2.2 equiv) in ethylene dichloride (60°C, 3 h) gives two products, 6-acetyl-l,4-dimethoxynaphthalene (30%) and l-hydroxy-2-acetyl-4-methoxynaphtha-lene (50%). Suggest a rationalization for the formation of these two products and, in particular, for the differing site of substitution in the two products. 

In the same way, the displacement of the unpaired electron over the whole molecules was observed for cation-radicals from Scheme 1.4d and 1.4e, in which 1,4-dimethoxynaphthalene units are syn- or anti-annealed to [2.2]paracyclophane (Wartini et al. 1998a, 1998b). In another study, the electron transfer between 1,4-dimethoxybenzene and 7,7-dicyanobenzoquinone methide moieties... 

Methoxynaphthalenes may be lithiated in their ortho or peri positions according to conditions (see Table 1 in Section LA). 1,4-Dimethoxynaphthalene, for example, perilithi-ates cleanly with f-BuLi (Scheme 67) ... 

In order to increase the n-n interaction with the aromatic guests, two molecular clips with naphthalene walls (compounds 8 and 9) were synthesized. These molecules had quite unexpected properties. Surprisingly, the clip with 1,4-dimethoxynaphthalene cavity walls (8) did not bind guest molecules [15]. The reason for this behavior became clear when the X-ray structure was solved [16] (Fig. 6). All four methoxy groups of 8 were found to point into the cavity, completely blocking the access of a potential guest to the carbonyl groups. A similar structure may also be present in solution. 

Using the standard procedures, 1,4-dimethoxynaphthalene is complexed at the less-substituted ring with high selectivity to give (42).68 Again, under conditions of minimum equilibration of anion addition, LiCMe2CN gave a mixture (after iodine oxidation) of the l,4-dimethoxy-f3-substituted and 1,4-dimeth-oxy-a-substituted products in the ratio 78 22. After equilibration, the a-substitution product was essentially the only product found (equation 37). 

A mixture of 20.0 g POCl3 and 22.5 g N-methylformanilide was allowed to stand at room temperature for 0.5 h which produced a deep claret color. To this there was added 9.4 g 1,4-dimethoxynaphthalene and the mixture was heated on the steam bath. The reaction mixture quickly became progressively darker and thicker. After 20 min it was poured into 250 mL H20 and stirred for several h. The solids... 

Reactions of 1,4-dimethoxynaphthalene and its 2-chloro, 2-bromo, and 2-(1,3-dioxolanyl) derivatives with BAIB/TMSX (X = C1, Br) combinations in dichloromethane result in acetoxylation, monohalogenation, or dihalogenation of the more activated ring (Scheme 26) [79]. Specific outcomes depend on the naphthalene derivative and reaction conditions. It is interesting that the 2-(1,3-dioxolanyl) derivative undergoes ipso-bromination with BAIB/TMSBr, and that this mode of reactivity was not observed with 2-(l,3-dioxolanyl)-l,4-di-methoxybenzene. These reactions are mechanistically diverse. Evidence was presented that bromination occurs after the formation of molecular bromine, and that chlorination probably follows a radical pathway involving the homo-... 

The radical anions of electron-deficient aromatic compounds and aromatic hydrocarbons, which are generated by photoinduced electron transfer, can be proto-nated by protic solvents or by the radical cations of amines to produce their neutral radicals [Eq. (7)]. Dispropotionation of the radicals yields the reduction products. The radical anions of 1,1-diphenylethene in the presence of 1,4-dimethoxynaphthalene as an electron donor is also protonated by protic solvents to give Markownikoff adducts [402,403] (Scheme 118). 

As mentioned in Sec. 15.2.3, benzylic radicals are obtained also from the cleavage of a nucleofugal group from the radical anion. This may lead again to benzylation, and it has been shown that irradiation of 1,4-dimethoxynaphthalene in the presence of substituted benzyl halides leads to benzylated naphthalenes (mainly in position 2) via benzyl radical/arene radical cation combination, which is analogous to the benzyl radical/radical... 

Figure 2 shows the structures of the bifunctional model systems l(n), (n=4,6,8,10,12), investigatedThe synthesis of these systems and a discussion of their electrochemical properties as well as of their electronic absorption and emission spectra have been given elsewhere (Oevering et al., 1987). These molecules contain a 1, 4-dimethoxynaphthalene unit as the photoexcitable electron donor (E./2 =+1.1 V vs. see in acetonitrile) and a 1,1-dicyano-vinyl moiety as a moderately powerful electron acceptor (Ev=-. l V) separated by an array of at least n C-C sigma-bonds. The centre-to-centre separation (Rc) and the edge-to-... 

With the 1,4-dimethoxynaphthalene ligand, cyano-stabilized anions (including cyanohydrin acetal anions) and ester enolates equilibrate even at low temperature and strongly favor addition at the a-position (C-5). The kinetic site of addition is also generally C-a. However, the 2-lithio-l,3-dithiane anion and phenyllithium do not equilibrate over the temperature range -78 to 0°C. The sulfur-stabilized anions favor addition at C-/3 (equation 119) 134,190 phenyllithium... 

While the addition/oxidation and the addition/protonation procedures are successful with ester enolates as well as more reactive carbon nucleophiles, the addition/acylation procedure requires more reactive anions and the addition of a polar aprotic solvent (HMPA has been used) to disfavor reversal of anion addition. Under these conditions, cyano-stabilized anions and ester enolates fail (simple alkylation of the carbanion), but cyanohydrin acetal anions are successful. The addition of a cyanohydrin acetal anion to l,4-dimethoxynaphthalene-Cr(CO)3 occnrs by kinetic control at C-/3 in THF/HMPA and leads to the O -diacetyl derivative after methyl iodide addition and hydrolysis of the cyanohydrin acetal. Monoacylation of 1,4-dimethoxynaphthalene-Cr(CO)3 has been achieved nsing the seqnence of reactions shown in eqnation (126). ... 

Formation of cycloadducts can be completely quenched by conducting the experiment in a nucleophilic solvent. This intercepts radical cations so rapidly that they cannot react with the olefins to yield adducts. In Scheme 54 the regiochemistry of solvent addition to I-phenylcyclohexene is seen to depend on the oxidizability or reducibiiity of the electron-transfer sensitizer. With ]-cyanonaphthalene the radical cation of the olefin is generated, and nucleophilic capture then occurs at position 2 to afford the more stable radical. Electron transfer from excited 1,4-dimethoxynaphthalene, however, generates a radical anion. Its protonation in position 2 gives a radical that is oxidized by back electron transfer to the sensitizer radical before being attacked by the nucleophilic solvent in position 1. Thus, by judicious choice of the electron-transfer sensitizer, it is possible to direct the photochemical addition in either a Markovnikov (157) or anti-Markovnikov (158) fashion (Maroulis and Arnold, 1979). 

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]. 

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