Naphthalene reductive alkylation

Additionally, it was found that the double reductive alkylation of the 2,5-diester 66 could be achieved under Birch conditions (Li/NH3) to produce the 3-pyrroline 67. On the basis of a mechanistic postulate that such reductions do not involve transfer of a proton from ammonia, the authors discovered that the same reduction could be performed in THF (no ammonia) with lithium metal and catalytic amounts of naphthalene as an electron shuttle, thereby making this reaction more practicable on a large scale <00TL1327>. 

This type of Birch reduction-alkylation also works in the naphthalene series36. Thus, the naphthalene carboxamides 10. when subjected to the standard Birch reduction-alkylation conditions, furnish a single set of diastereomers 11 (d.r. >95 5 by ]II and 13C NMR no experimental details given)36. 

As already mentioned, several investigators have pointed out that naphthalene or tetrahydrofuran may be incorporated into the coal product (9, 10, 11), In this work we found that chromatographic procedures could be used to separate unbound naphthalene and its reductive alkylation products from the coal alkylation products. The spectroscopic work indicates that the principal resonances of naphthalene and tetrahydrofuran are absent from the butylated coals. Moreover, the mass balance shows that no important quantity of naphthalene or tetrahydrofuran could be incorporated. We supplemented this negative evidence by a comparison of the reaction products obtained from the same coal in a reaction in liquid ammonia. In the most pertinent case the Illinois No. 6 coal was treated with potassium in liquid ammonia. The polyanion was alkylated with butyl iodide. The product distribution obtained by GPC and the spectroscopic properties of these fractions were very closely related to the properties of the reaction products obtained in the reaction with naphthalene in tetrahydrofuran. Recently Larsen and his group found that neither " C-labeled naphthalene nor tetrahydrofuran was incorporated in chemically significant amounts in the coal products separated from the reaction mixture by chromatography (12). 

Proton and Carbon NMR Spectra. The alkylated coal products were separated from the reductive alkylation products of naphthalene. The coal products then were separated into several fractions by chromatography on Styragel. The proton and carbon NMR spectra of the individual fractions were recorded. 

Our results on the reductive alkylation of coal offer insights into proposed analogies between coal chemistry and graphite chemistry (37). Graphite, as the largest polynuclear aromatic compound, can be reduced by anions of all other polynuclear aromatic compounds in fact, this observation has been exploited to synthesize intercalation compounds (38j. Although the added electron density of these compounds is predominantly on the carbon planes, these infinite aromatic anions possess chemistry distinct from that of molecular-basis aromatic anions. While napthalene anion will react with water to form a mixture of 1,4-dihydro-naphthalene and naphthalene, the graphite anion is inert to water (39-42) ... 

The Sternberg reductive alkylation procedure was carried out as described in the literature (i, 2j, employing up to a 40 1 ratio of alkali metal to naphthalene (molar basis). The model reactions involved mixtures containing 5 g (39 mmol of naphthalene, 2 g (87 mmol) of sodium, and 25 mL of tetrahydrofuran. Tetra-hydrofuran was obtained from both Fisher and Aldrich and was either distilled from lithium-aluminum hydride or dried over sodium. No differences in the decomposition behavior was noted for the two drying procedures furthermore, the presence or absence of the inhibitor butylated hydroxy toluene did not affect the decomposition. 

The process now known as reductive alkylation of rc-conjugated anions (quenching of anions) is as old as the preparation of the ions themselves5). The highly colored solutions obtained by the addition of alkali metals to solutions of aromatic hydrocarbons in ether were reacted with electrohpiles such as protons or alkyl halides (Scheme 2). The products of such a process are reduced hydrocarbons. The Birch reduction is one example oT such a process, reaction of an anion with an alkyl halide leading to an alkylated reduced hydrocarbon is another example 165). The complexity of the quenching experiments is demonstrated by the naphthalene radical anion 150-1581... 

Table I. Reductive Alkylation of Anthracene, Naphthalene, and Biphenyl in Metal-Ammonia Solutions...

In principle, the reductive alkylation of coal involves treatment of coal with an alkali metal in tetra-hydrofuran in the presence of naphthalene whereby a coal polyanion is produced that is capable of undergoing further reaction with, say, an alkali halide. The resnlting product has been presumed to be the alkylated coal but the relatively straightforward chanistry is, in fact, a complex sequence of reactions. For example, ether bridges are also cleaved under the conditions of the reaction as are carbon bonds. That the former can happen makes the resulting product mix somewhat more complex than if ethers were not cleaved but the cleavage of carbon-carbon bonds ensures the complexity of the product mix as well as the chemistry involved in the process. 

The concept of coal alkylation has been expanded to a variety of studies relating to coal structure (Sternberg et al., 1971 Sternberg and Delle Donne, 1974 Wachowska, 1979 Alemany et al., 1981 Wender et al., 1981 Handy and Stock, 1982). This is, essentially, a method of reductive alkylation, which, as a first step, necessitates reacting the coal with metallic potassium and naphthalene in... 

Substitution. Substitution products retain the same nuclear configuration as naphthalene. They are formed by the substitution of one or more hydrogen atoms with other functional groups. Substituted naphthalenes of commercial importance have been obtained by sulfonation, sulfonation and alkah fusion, alkylation, nitration and reduction, and chlorination. 

Reactions other than those of the nucleophilic reactivity of alkyl sulfates iavolve reactions with hydrocarbons, thermal degradation, sulfonation, halogenation of the alkyl groups, and reduction of the sulfate groups. Aromatic hydrocarbons, eg, benzene and naphthalene, react with alkyl sulfates when cataly2ed by aluminum chloride to give Fhedel-Crafts-type alkylation product mixtures (59). Isobutane is readily alkylated by a dipropyl sulfate mixture from the reaction of propylene ia propane with sulfuric acid (60). 

Arylalkylsulfones ate important intermediates obtained by alkylation of arylsulfinic acids. The latter ate obtained by reduction of the corresponding sulfonyl chloride. This reduction process is simple and of general appHcation involving the addition of the isolated sulfonyl chloride paste to excess aqueous sodium sulfite followed by salting-out the product and isolation. With mote rigorous reduction conditions, such as zinc/acid, sulfonyl chlorides ate reduced through to aryknercaptans, eg, 2-mercaptonaphthalene is manufactured from naphthalene-2-sulfonyl chloride. 

The addition of alkyl halides to aromatic anion radicals, generated by alkalimetal reduction in ethereal solvents, was already known in the 1950s [201] and was reviewed by Garst in 1971 [202]. The first electrochemical analogue was observed by Lund etal. [203]. These authors cathodically reduced hydrocarbons such as naphthalene, anthracene, stilbene [145, 146], and pery-lene [147-150] in the presence of alkyl halides and isolated hydrogenated and alkylated products. Similar reactions are observed when the halides are replaced by ammonium or sulfonium [204]. 

Lund and coworkers [131] pioneered the use of aromatic anion radicals as mediators in a study of the catalytic reduction of bromobenzene by the electrogenerated anion radical of chrysene. Other early investigations involved the catalytic reduction of 1-bromo- and 1-chlorobutane by the anion radicals of trans-stilhene and anthracene [132], of 1-chlorohexane and 6-chloro-l-hexene by the naphthalene anion radical [133], and of 1-chlorooctane by the phenanthrene anion radical [134]. Simonet and coworkers [135] pointed out that a catalytically formed alkyl radical can react with an aromatic anion radical to form an alkylated aromatic hydrocarbon. Additional, comparatively recent work has centered on electron transfer between aromatic anion radicals and l,2-dichloro-l,2-diphenylethane [136], on reductive coupling of tert-butyl bromide with azobenzene, quinoxaline, and anthracene [137], and on the reactions of aromatic anion radicals with substituted benzyl chlorides [138], with... 

In one of the more frequently utilized Birch reactions (the reduction of alkyl/alkoxy-substituted naphthalenes), two reduction products are obtained as shown in Scheme 7.10. The acidity of the alcohol employed for protonation determines the ratio of these two products. For example, the ratio of the product hydrogenated in the substituted fused ring to the product hydrogenated in the unsubstituted fused ring was compared for methanol... 

Dialkyl ditellurides (general procedure A mixture of powdered Te (3.58 g, 28 mmol), Na chips (0.65 g, 28 mmol) and naphthalene (0.36 g, 2.8 mmol) in anhydrous THF (25 mL) is refluxed under Nj and stirred for 1 h. During this time all the sodium is consumed and the mixture turns a light brown colour. The solution is stirred for an additional 3 h to ensure the complete reduction of Te, the temperature is then lowered to 10°C and the alkyl hahde (28 mmol) is added dropwise for 30 min with stirring. After an additional hour of stirring at room temperature, the reaction mixture is filtered, the solvent evaporated and the residue distilled under vacuum, giving the pure ditelluride (R=Et (85%), n-Pr (90%), n-Bu (90%), MeOCHjCHj (60%)). 

Since different reactivity is observed for both the stoichiometric and the catalytic version of the arene-promoted lithiation, different species should be involved in the electron-transfer process from the metal to the organic substrate. It has been well-established that in the case of the stoichiometric version an arene-radical anion [lithium naph-thalenide (LiCioHg) or lithium di-ferf-butylbiphenylide (LiDTBB) for using naphthalene or 4,4 -di-ferf-butylbiphenyl (DTBB) as arenes, respectively] is responsible for the reduction of the substrate, for instance for the transformation of an alkyl halide into an alkyllithium . For the catalytic process, using naphthalene as the arene, an arene-dianion 2 has been proposed which is formed by overreduction of the corresponding radical-anion 1 (Scheme 1). Actually, the dianionic species 2 has been prepared by a completely different approach, namely by double deprotonation of 1,4-dihydronaphthalene, and its X-ray structure determined as its complex with two molecules of N,N,N N tetramethylethylenediamine (TMEDA). ... 

The classical preparation of alkyllithium compounds by reductive cleavage of alkyl phenyl sulfides with lithium naphthalene (stoichiometric version) was also carried out with the same electron carrier but under catalytic conditions (1-8%). When secondary alkyl phenyl sulfides 73 were allowed to react with lithium and a catalytic amount of naphthalene (8%) in THF at —40°C, secondary alkyllithium intermediates 74 were formed, which finally reacted successively with carbon dioxide and water, giving the expected carboxylic acids 75 (Scheme 30) °. 

Other methods that use 55 anions as precursor for the synthesis of fullerene-derivatives usually involve chemical formation of the anion. Alkylation of 55 has been accomplished, e.g. by reduction with propanethiol and potassium carbonate in DMF [91,92], sodium methanethiolate in acetonitrile [93], the naphthalene radical anion in benzonitrile[94], potassium naphthalide [95] or simply with zinc [96]. 

Under these conditions, a broad range of polyfunctional alkyl iodides are converted to the corresponding organozinc halides in high yields . In the case of primary alkyl iodides, the insertion occurs at 40-50 °C whereas secondary alkyl iodides already react at 25-30°C. Secondary alkyl bromides also react under these conditions , but primary alkyl bromides are usually inert with this type of activation and much better results are obtained by using Rieke zinc L Thus, the reduction of zinc chloride with finely cut lithium and naphthalene produces within 1.5 h highly reactive zinc (Rieke zinc). 

The synthesis of organozinc compounds by electrochemical processes from either low reactive halogenated substrates (alkyl chlorides) or pseudo-halogenated substrates (phenol derivatives, mesylates, triflates etc.) remains an important challenge. Indeed, as mentioned above, the use of electrolytic zinc prepared from the reduction of a metal halide or from zinc(II) ions does not appear to be a convenient method. However, recent work reported by Tokuda and coworkers would suggest that the electroreduction of a zinc(II) species in the presence of naphthalene leads to the formation of a very active zinc capable of reacting even with low reactive substrates (equation 23)11. 

Notably, Zn2+ ions are more easily reduced than naphthalene. This indicates that the electroreduction of the latter is very likely achieved on a recovered electrolytic zinc cathode. What happens under these conditions So far, no data allow us to answer this question. The only information is the experimental observation of a characteristic transient color of the naphthalene anion radical indicating the reduction of this hydrocarbon, simultaneously with the reduction of Zn2+, owing likely to a too high current density set at the cathode11. Moreover, the presence of an alkyl halide under such conditions would lead to its reduction on the zinc deposit, and this reduction would occur more easily than the reduction of naphthalene according to complex processes (equation 25). 

Lithium naphthalenide has been used for reductive lithiation of thioketals (8, 306 9, 284), but has the disadvantage that naphthalene is sometimes difficult to separate from final products of alkylation. In such cases, lithium I -(dimethylamino)-naphthalenide can be used advantageously since dimethylaminonaphlhalene is removed from reaction mixtures by extraction with dilute acid.1... 

Reductive removal of fluorine from alkyl fluorides requires a potent reducing agent and so is not normally encountered However, hydrogenolysis of an unactivated carbon-fluorine bond in, for example, 3 p-fluorocholestane has been efficiently accomplished in 88% yield with a solution of potassium and dicyclohexyl 18 crown-6 in toluene at 25 °C [/] Similarly, sodium naphthalene in tetrahydrofuran converts 6 fluorohexene-1 and 1-fluorohexane to hydrocarbons in 50% yield at 25 °C over a 7-h period [2]... 

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