Anthracene reductive alkylation

Reductive alkylation is one of several reactions that occurs when l,l-dichloro-2,2,3,3-tetra-methylcyclopropane and 7,7-dichlorobicyclo[4.1.0]heptane are exposed to magnesium-anthracene in tetrahydrofuran. The best results were obtained with 7,7-dichloro-bicyclo[4.1.0]heptane, which gave 9-(bicyclo[4.1.0]hept-7-yl)-9,10-dihydroanthracene and 9,10-bis(bicycIo[4.1.0]hept-7-yl)-9,10-dihydroanthracene in 44 and 34% yield, respectively. 

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

Anthracene undergoes reductive alkylation on treatment with sodium bis-(2-methoxyethoxy)aluminium hydride, the spiro-compound (91) being one of the... 

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... 

The allylic sulfonyl group is regioselectively cleaved in the presence of the alkyl-sulfonyl group by indirect reduction with anthracene as a mediator (Fig. 24) [125]. 

Such polycyclic aromatic hydrocarbons as anthracene or heteroaromatics as acridine, phenazine and 2,4,5-triphenyl oxazole act as Jt-donors for the Jt-acceptors AN and alkyl methacrylates [50-53]. Again, the interaction of the donor excited states with vinyl monomers leads to exciplex formation. But, the rate constants (k ) of these quenching processess are low compared to other quenching reactions (see Table 1). The assumed electron transfer character is supported by the influence of the donor reduction potential on the k value (see Table 1), and the detection of the monomer cation radicals with the anthracene-MMA system. Then, the ion radicals initiate the polymerization, the detailed mechanism of which is unsolved,... 

Electrophilic reactions on the electron-deficient anthraquinone are normally not possible. However, in 1936 Marschalk described the facile alkylation of the anthraquinone nucleus by aldehydes after reduction of the quinone to the electron-rich hydroquinone using dithionite [34]. This strategy might be called a redox Umpolung , since the chemical reactivity of the anthracene core is reversed by the redox reaction. 

Reduction of aromatic hydrocarbons. Anthracene is reduced quantitatively to 9,10-dihydroanthraccncby sodium in HMPT with THF as cosolvent. The reaction has been extended to benzanthracene, tetracene, and 9-alkyl- and 9,10-dialkylanthraocnes to give the corresponding mejo-dihydro derivatives. Water or methanol diluted in THF is used as the proton source. ... 

Fluorene has been reported to afford the 3,9a-dihydro product, but it is almost certain that this is the 2,4a-dihydro isomer (55 = 1) by analogy with biphenyl. 9,10-Dihydrophenanthrene (56) is reduced as expected to (55 n = 2), but spontaneously reverts to the starting material on standing. These systems do not require the presence of alcohol for reduction and it is consequently possible to alkylate the intermediate anions with alkyl halides, as (56) gives (57). These products are much more stable and structural analysis is simplified accordingly oxidation of the doubly allylic methylene occurs readily to afford the dienone (58 Scheme 7). Dienones of this type have potential as intermediates for the synthesis of natural products. Anthracene and phenanthrene are both readily reduced in the central ring to form the 9,10-di-hydro derivatives as might be expected, but to avoid further reduction it is necessary to have an iron salt present. Further examples are reviewed elsewhere. ... 

More work with other aromatic compounds will be necessary to verify this conclusion. However, the results for anthracene certainly suggest that the results obtained in the reaction are strongly dependent upon the aromatic substrate. The results obtained thus far also suggest that the reduction and subsequent alkylation of large polycyclic molecules, e.g., compounds such as pyrene, are not the most critical factors for the formation of soluble alkylation products. Studies of the molecular weight distributions and spectroscopic properties of the alkylation products obtained with different metals and different electron transfer agents are underway to resolve this issue. 

Aromatic hydrocarbons can be reduced to cycloalkenes by calcium dissolved in a mixture of methylamine and ethylenediamine. For example, calcium reduction of p-xylene (57) and anthracene (59) gives 1,4-dimethyl-l-cyclohexene (58) or decahydroanthracene (60) in 84% and 85% yield, respectively (Scheme 4.16). Calcium-amine combinations are different from lithium-amine systems in that they have little or no propensity to reduce internal double bonds despite the large excess of calcium employed. A grayish white precipitate, seemingly calcium alkyl amide. 

---