Naphthoxide anion

Alkylations in dry media of the ambident 2-naphthoxide anion were performed under the action of focused microwave activation. Whereas the yields were identical to those obtained under the action of A for benzylation, they were significantly improved under microwave irradiation conditions for the more difficult n-octylation (a less reactive electrophilic reagent). No change in selectivity was observed, however, indicating the lack of influence of ionic polarization [94],... 

The absence or weakness of the microwave effect was assumed to be related to loose ion pairs involving the soft naphthoxide anion in the GS and a small change in polarity in an early TS. When the TS occurred later along the reaction coordinates (e.g. for n-octylation requiring a higher temperature), more polarity is developed and, consequently, the microwave effect could appear (Eq. (42) and Tab. 3.17 limited here to the lithiated base). 

The iron(II)-iron(III) form of purple acid phosphatase (from porcine uteri) was kinetically studied by Aquino et al. (28). From the hydrolysis of a-naphthyl phosphate (with the maximum rate at pH 4.9) and phosphate binding studies, a mechanism was proposed as shown in Scheme 6. At lower pH (ca. 3), iron(III)-bound water is displaced for bridging phosphate dianion, but little or no hydrolysis occurs. At higher pH, the iron(III)-bound OH substitutes into the phosphorus coordination sphere with displacement of naphthoxide anion (i.e., phosphate hydrolysis). The competing affinity of a phosphomonoester anion and hydroxide to iron(III) in purple acid phosphatase reminds us of a similar competing anion affinity to zinc(II) ion in carbonic anhydrase (12a, 12b). 

Argriello, J.E. and Penenory, A.B. (2003) Fluorescent quenching of 2-naphthoxide anion by aliphatic and aromatic halides, mechanism and consequences of electron transfer reactions. Journal of Organic Chemistry, 68, 2362-2368. 

Chlorobiphenyl and 2-chloronaphthalene were irradiated in methanol containing / -naphthol and sodium methoxide and found to undergo photodechlorination408. The key step in the mechanism is electron transfer from photoexcited naphthoxide anion 133 to the aryl halide. The naphthoxyl radical is supposed to take up a hydrogen atom from the solvent and, by subsequent deprotonation, the naphthoxide anion is regenerated (equation 111). 

By formation of the naphthoxide anion with NaH prior to the reduction, slightly higher yields are obtained. 

The photochemical substitution reactions of 2-naphthoxide anion and o-halophenol (X = Br, I) in an aqueous sodium sulfite solution were also reported Photosubstitution of the sulfo group for hydrogen is observed under irradiation of sulfonated derivatives of hydroquinone. Benzo[a]phenanthridine-5-ones (156) (159) were synthesized by photo-induced substitution and cycloaddition of 3-chloroisoquinolin-l-ones... 

Photoinitiation is not the only access to this chemistry, e.g., cathodic induced reduction or the use of alkali metals or other inorganic reducing reagents are also possible, but irradiation often is advantageous for preparative purposes. Since this is a chain process, the use of low-power lamps or a low quantum yield initiation step are not necessarily a limitation. Due to the requirement of a fast cleavage at the radical anion stage, aryl halides are by far the most used reagents, in particular iodides and, to a lower extent, bromides. Nucleophiles are carbanions from sufficiently acidic hydrocarbons, e.g., 1, 3-diphenylindane, fluorene or triphenylmethane [35-37] or, more commonly enolates from ketones [38], esters [39], MA -dialkylamides [40], nitriles [41]. C-C bond formation is obtained also with phenoxide or naphthoxide anions [42,43]. A few representative examples of synthetic applications of the S l... 

The irradiation of 1-naphthoxide anion in the presence of methoxide also gives a photodimer (301), by nucleophilic photosubstitution.1-Alkoxynaphthalene undergoes thiocyanation by the copper(ii) thiocyanate method to give (302), the... 

Initiation of the reaction of l-chloro-2-naphthoxide anion with NajSO, has been proposed to occur by ET between the excited triplet state of the substrate and its ground state. This reaction can be dye-photoinitiated-" or initiated by visible light with a Ru complex as sensitizer and a Co complex as the intermediate electron carrier.- - For the 1-bromo derivative, photohomolytic CBr bond dissociation is proposed. "... 

Kornblum et al. (1963) demonstrated that O- vs. C-alkylation (24) of yS-naphthoxide ion (an ambident ion) is markedly solvent dependent. For example, the reaction with benzyl bromide conducted in dimethylformamide gave 97% O-alkylated product, whereas in water 81% C-alkylated product resulted. The difference is attributed to changes in the solvation of ambident anions. The course of the reaction is also influenced by water concentration in... 

Alkoxide or aryloxide anions are also reputed to be inactive in Sr I reactions. There is, however, one example of such a reaction at an sp carbon the nitro-derivative of 4-nitrocumyl reacts with phenoxide and 1-methyl-2-naphthoxide ions yielding the corresponding ethers (Kornblum et al., 1967). A similar reaction has been reported for halobenzenes in t-butyl alcohol upon stimulation by sodium amalgam (Rajan and Sridaran, 1977). This reaction could not, however, be reproduced (Rossi and Pierini, 1980) and other attempts to make phenoxide ions react at sp carbons have been equally unsuccessful (Ciminale et al, 1978 Rossi and Bunnett, 1973 Semmelhack and Bargar, 1980). It has been found, more recently, that phenoxide ions react with a series of aryl halides under electrochemical induction, but that the coupling occurs at the p- or o-phenolic carbon rather than at the phenolic oxygen (Alam et al, 1988 Amatore et al, 1988). This is... 

Not all nucleophilic displacement reactions require lightly substituted onium ion catalysts for activity. For alkylation of 2-naphthoxide ion with benzyl bromide (Eq. (6)) 40-100% RS, 2% CL polystyrene catalysts 15 and 16 work well54). A 51 % RS catalyst 11 gave good yields in reactions of anionic oxygen and sulfur nucleophiles with alkyl halides 91). 

The data in Table 7 obtained with equimolar amounts of the polymeric catalysts and the 2-naphthoxide ion should be more reliable because all of the reactive anion is contained within the polymer. These conditions (expts 7-9) gave 100 % O-alkylation, indicating that the active site environment of the polystyrene-bound tri-n-butylphos-phonium ion/naphthoxide ion pair or aggregate is aprotic even with the 60%RS polymer. However, the common benzyltrimethylammonium ion found in commercial ion exchange resins is more hydrophilic, giving both C- and O-alkylation (expts 10 and 11 of Table 7). 

In the reaction of 1-naphthoxide ions, a mixture of 2- and 4-aryl-, along with 2,4-diaryl-l-naphthol, is formed. However, substitution occurs only at C4 with the 2-Me-substituted anion (50-70% yields) [1[. On the other hand, 2-naphthoxide ions react with ArX to give substitution only at Cj of the naphthalene ring [32, 33]. The reactivity of the 2-naphthoxide ions allows the synthesis of naphthylpyridines, naphthylquinolines, and naphthylisoquinolines via their coupling reactions with the corresponding halo arenes, in good to excellent yields (50-95%) [33], The photostimulated reaction between 2-naphthoxide ions and l-iodo-2-methoxy-naphthalene was explored in liquid ammonia, as a novel approach to the synthesis of [1,1 ] binaphthalenyl-2,2 -diol (BINOL) derivatives (Scheme 10.23). This procedure has also been applied to the synthesis of BINOL in moderate yield (40%), which represents the first report of an SRN1 reaction in water [34]. 

The substitution of l-chloro-2-naphthoxide ion by sulfite ion in water can also be initiated by visible light (436 nm) with the complex [Ru(bipy)2]Cl as the sensitizer and the complex [Co(bipy)3](C104)2 as the intermediate electron carrier3315. Another possibility is a dye photoinitiated reaction. In the latter example, the excited triplet of the dye (fluorescein, eosine or erythrosine) receives an electron from S03 2 whose radical anion (S03) reacts with halonaphthoxides to give finally the substitution product33c. 

More recent studies, however, have proved that these anions, mainly di-7-butyl substituted phenoxides and 1- and 2-naphthoxide ions, are excellent nucleophiles under electrochemical or photostimulated conditions. These anions behave as bidentate nucleophiles and couple with radicals through the carbons of their aromatic ring. This has been proved to be a powerful route to biaryls unsymmetrically substituted by EWG and electron-acceptor groups, which are of interest in non-linear optics, as well as in the synthesis of cyclic compound (Section V.E.2). 

The regiochemistry of the reaction of phenoxide and naphthoxide ions with radicals was explained on the basis of the perturbation theory of the frontier MO involved in the coupling reaction, which are the HOMO of the nucleophile and the SOMO of the radical2626. The position of the coupling depends on the charge distribution in the HOMO of the nucleophile. Perturbation theory and thermodynamic stability of the formed radical anions follow the same tendency. 

In the photostimulated reaction of 2-naphthoxide ion (198) with an o-dihalobenzene, an aromatic a radical may be formed very close to the oxygen functionality along the chain propagation cycle of the S l mechanism. This spatial proximity and the fact that the intramolecular coupling between the two moieties will form a relatively stable radical anion will favour the reaction between both reactive centres. Thus in the photostimulated reaction of o-dihalobenzenes with 198 in liquid ammonia, the formation of the monosubstitution 351 and of the cyclization product 352 were reported in yields that depend on the substrate and on the reaction conditions (equation 205)346. 

Trapping agents, such as malonate anions, naphthoxides, and phosphines have been used to determine the concentration of chain carriers in controlled/living and other carbocationic systems [85,249,250]. These strong nucleophiles react with all sufficiently electrophilic species, including not only carbocations but also onium ions and covalent esters. Thus, the discussed measurements can provide only the total concentration of active and dormant end groups. In principle, the kinetics of formation of the product in the trapping experiments could resolve more and less active species but only if they are present at comparable concentrations. As discussed before, carbocations are present in ppm quantities in comparison with dormant species. 

A mechanism for this reaction has been proposed and is summarized in Sch. 10. The catalyst 64 is thought to be bifunctional with the aluminum center operating as a Lewis acid and the lithium naphthoxide operating as a Lowry-Brpnsted base. It was envisaged that the aldehyde coordinates with the aluminum to give the complex 69 and deprotonation of the dimethyl phosphite then gives the aggregate 70 in which the phosphite anion is positioned for P-alkylation of the aldehyde that will occur selectively from the si face when the catalyst is prepared from (f )-BINOL. 

Chloro-l-hydroxynaphthalene is converted into the sulphonate 246 on eosin-sensitized irradiation in the presence of sodium sulphite. A study of the chain substitution of the chloro group in 4-chloro-l-hydroxynaphthalene by aqueous sodium sulphite has shown that two mechanisms for the photoinitiation have been identified and two intermediates have been detected a radical anion of 4-chloro-l-naphthoxide and the sulphite radical anion. Thus, an SjjajI mechanism is suggested and is one that involves reaction with the radical anion of sulphite. An example of the S n 1 process between a phenol and the (2-cyanoaryl)azo-f-butylsulphides has been reported. The 1 reactivity of several compounds (Scheme 27) have demonstrated that 247 is a product however, this is also photochemically reactive and is converted into the cyclic ether 248 . 

The tropylium ion attacks phenols in the presence of alkali [79, 84-86]. Thus with phenol itself a tropylphenol is formed which has been shown to consist mainly of the pam-isomer plus a small amount of the ortho-isotaer. Reaction probably proceeds by direct attack of the tropylium ion on the phenoxide anion. In the case of 8-naphthol a more complicated reaction ensues in which the naphthoxide ion is oxidised as well as substituted, and the isolated products are benzaldehyde and 2-hydroxy-l,4-naphthaquinone [85]. 

The anions derived from phenols are bidentate nucleophiles and can react through of the O- or the C-atoms. For example, the 2-naphthoxide ions 65 react with ArX to give substitution only at C-1 of the naphthalene ring [61]. In this reaction, the intermediated Ar radical couples in C-1 of 65 to yield the radical anion 66, which by ET gives the product 67 that after tautomerization yields the more stable products 68 (Eq. 10.25). The rates of reactions of 2- and 4-anisyl and 2-methoxy-l-naphthyl radicals with 65 were determined (10 -10 M s" ) using an indirect method, a competition of the coupling reaction with the H-atom abstraction from the DMSO [62] ... 

The phase transfer method has also been used in the preparation of a variety of phenolic ethers [5]. It is interesting that alkylation of phenoxide anions generally yield products of both C and 0-alkylation with one favored to a greater or lesser extent depending on solvent. Sodium 2-naphthoxide, for example, exclusively C-benzylates in such hydrogen bonding solvents as ethanol [6], whereas 0-alkylation is favored in tetrahydrofuran. As the size of the cation associated with 2-naphthoxide is increased (for example from Li" to R4N ), 0-alkylation tends to be favored. Consistent with these observations is the report that 2-naphthol 0-alkylates under phase transfer conditions [5]. The successful 0-alkylation of the isomeric nitrophenols and salicyl-aldehyde are also noteworthy. These observations are consistent with the view that... 

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