Diels-Alder reaction with fullerene

SCHEME 12. Diels-Alder reactions with fullerenes as dienophiles... 

Wang and co-workers also evaluated the reactivity of 9-substituted anthracene in Diels-Alder reactions with fullerene. Corresponding adducts were prepared in high yields under solvent-free conditions using the high-speed vibration milling technique (Scheme 8.14). ... 

Diels-Alder reaction of fullerenes with complex dienes type 52 (Figure 2.6) which have a 2,3-bis-(methylene) bicyclo[2.2.2]octane unit [49]. 

Cheng and coworkers142 reported the first Diels-Alder reactions of fullerenes with dienes having an electron-withdrawing group at C(l). The reactions with [60]fullerene proceeded at elevated temperatures to afford the corresponding adducts with moderate yields. The adducts appeared to be more stable than the adducts of electron-rich dienes. 

A review of Diels-Alder reactions of fullerenes with acyclic and cyclic dienes has been presented. The addition of substituted pyrimidine o-quinodimethanes (75) to [60]fullerenes yields novel organofullerenes (76) bearing a pyrimidine nucleus covalently attached to the Ceo cage (Scheme 26). The Diels-Alder dimerization of cyclopenta[/]phenanthrene (77) with isobenzindene (78) yields the dimer (79) in 85% yield (Scheme 27). Further evidence has been supplied to support an early reorganization of the r-network in the dimerization of 2-methoxycarbonylbuta-1,3-diene. The Lewis acid-catalysed Diels-Alder reactions of acrylate derivatives of new carbohydrate-based chiral auxiliaries with cyclohexadiene show excellent endo. exo... 

Scheme 8.14 Diels-Alder reactions of fullerene with a 9-substituted anthracene.

Methylene-1,3-dioxepanes (34) and (36) were prepared by reaction of oxaphosphoranes (33) and (35) with paraformaldehyde (Scheme 5) <93TL4233>. Geometric isomers of compounds (37) and (38) (only (Z)-isomer depicted) have found interest in the chemistry of the antibiotic bicyclomycin <78JA6786,92JOC3662>. Diene (39) was studied in the Diels-Alder reaction with buckminster fullerene <95JOC8330>. 

Fullerenes can also be involved in [4 + 2] cycloaddition reactions (also called Diels-Alder reaction) with 1,3-dienes added. Here, the fullerene acts as an electron-deficient dienophile and addition takes place on a [6,6]-junction (Scheme 2.1d). Although this reaction allows the control of the degree of functionalization, [4 -i- 2] adducts are not stable and the reaction is in most cases thermally and photochemically reversible. 

AMI calculations of the addition of o-quinodimethanes with Ceo show that the mechanism is concerted. The Diels-Alder reaction between fullerene (Ceo) and Danishefsky s diene proceeds via a stepwise mechanism involving a single-electron transfer from the diene to the fullerene. ... 

Mikami, K., Matsumoto, S., Tonoi, T, and Okubo, Y, Solid state photochemistry for fullerene functionalization solid state photoinduced electron transfer in the Diels-Alder reaction with anthracenes, Tetrahedron Lett., 39, 3733, 1998. 

Diels-Alder reactions of butadienes 13 and 2,3-di-w-propylbutadiene 14 with [60]-fullerene 15 led to several fullerene derivatives [15-17] (Scheme 2.10). Dienes 13 and 14 bore electron-donating groups, but the reactions also occurred with electron-withdrawing substituents due to the sufficiently low-energy LUMO of Ceo-... 

Bis-o-quinodimethanes have also been used to functionalize [60]-fullerene by Diels Alder reaction. An example is the preparation of main-chain polymers with incorporated [60]-fullerene units [48] illustrated in Scheme 2.20. Cycloaddition of bis-diene 50 generated in situ from bis-sulfone 49 with [60]-fullerene leads to an oligomer mixture 51. Another type of functionalization is based on the... 

Exohedral functionalization of [60]-fullerene by [4 -i- 2] cycloadditions. Diels-Alder reactions of [60]-fullerene with electron-rich 2,3-dioxysubstituted-1,3-butadienes [146]... 

The low solubility of fullerene (Ceo) in common organic solvents such as THE, MeCN and DCM interferes with its functionalization, which is a key step for its synthetic applications. Solid state photochemistry is a powerful strategy for overcoming this difficulty. Thus a 1 1 mixture of Cgo and 9-methylanthra-cene (Equation 4.10, R = Me) exposed to a high-pressure mercury lamp gives the adduct 72 (R = Me) with 68% conversion [51]. No 9-methylanthracene dimers were detected. Anthracene does not react with Ceo under these conditions this has been correlated to its ionization potential which is lower than that of the 9-methyl derivative. This suggests that the Diels-Alder reaction proceeds via photo-induced electron transfer from 9-methylanthracene to the triplet excited state of Ceo-... 

Keywords Diels-Alder reaction of polymer supported cyclopentadiene with fullerene... 

The scope of the microwave technique in the preparation of fullerene derivatives was determined in the well known Diels-Alder reaction of C6o with anthracene (1) [71], which has been reported to occur under thermal conditions (13% [71a], reflux, toluene, three days 25% [71b], reflux, benzene, 12 h) (Scheme 9.22). In addition to 76, multiply-substituted adducts that undergo cycloreversion to the starting materials were formed. 

Novel pyrazine-containing cydoadducts 80a-c were synthesized by Diels-Alder reaction of [60]fullerene with the corresponding 2,3-bis(bromomethyl)pyrazine derivatives 79a-c (Scheme 9.23) [73] the 2,3-pyrazinoquinodimethanes were trapped as the Diels-Alder adducts by reaction with [60]fullerene under reflux in o-dichloroben-zene (ODCB) as solvent with classical heating and under the action of microwave ir-... 

Diels-Alder reactions have been used to synthesize and functionalize polymers, as reported by several groups. Rotello and coworkers112, for example, covalently attached [60]fullerene to furan and cyclopentadiene substituted resins. The reaction with the furan substituted resin proved reversible. The resin was recovered by heating the fullerene functionalized resin. 

The photo-induced single and double Diels-Alder reactions between [60]fullerene and 9-methylanthracene (212) which gave 213 and 214 were performed in the solid state by Mikami and colleagues (equation 60)141. The Diels-Alder reaction was considered to proceed following a photo-induced electron transfer from 9-methylanthracene to fullerene. The higher ionization potential of anthracene should explain its inreactivity toward the cycloaddition reaction with [60]fullerene. 

In analogy to olefins, Cjq undergoes a broad variety of cycloadditions (see Chapter 4 and Scheme 14.3). In many cases cycloadducts of Cjq exhibit the same stability as the corresponding non-fullerene based adducts. These reactions are very useful for the introduction of fimctionat groups. Among the most important cycloadditions are [4-1-2] cycloadditions such as Diels-Alder and hetero-Diels-Alder reactions, where Cjq reacts always as dienophile, [3-1-2] cycloadditions with 1,3 dipoles, thermal or photochemical [2-1-2] cycloadditions, [2-t-l] cycloadditions and others, for example, [8-1-2] cycloadditions. Among these general reactions several examples deserve special attention, since they reflect characteristic chemical properties of Cjq [36] ... 

The thermal Diels-Alder reaction ([4 + 2] cycloaddition) is widespread in the synthesis of fullerene derivatives. In contrast, only a few examples of the photochemical Diels-Alder reaction in solution or in the solid state are known. The first example is described by Tomioka and coworkers [249], Irradiation of ketone 73 and C6o at 10°C with a high pressure mercury lamp through a Pyrex filter led to the formation of 61-hydroxy-61-phenyl-l,9-(methano[l,2]benzenomethano) fullerene 75 (Scheme 29). This compound is unusually unstable and yields the monoalky 1-1,2-dihydrofullerene 76 either by silica gel chromatography or upon heating. 

The aziridinofullerenes and azafulleroids obtained by Mattay et al. were subjected to further reactions to yield fullerene adducts of the second generation. As a model compound 4-methyl-l,2,4-triazoline-3,5-dione (NMTAD) 187, which is one of the most reactive dienophiles for Diels-Alder reactions, was selected. Sheridan et al. studied the photoinduced [4 + 2] cycloadditions of NMTAD to arenes [295], With alkenes, however, NMTAD reacts in photoinduced cycloadditions in a [2 + 2] fashion under formation of diazetidines [296], Both the sulfonyl-azafulleroids (185) and aziridinofullerene (186) were irradiated at 420 nm to give both the same [2 + 2] cycloadduct 186 (Scheme 71) [291], This indicates that at a certain stage rearrangements must be involved. 

Recently, the reaction of masked ortho-benzoquinone [92] with C60 was tested [93]. The [4+2] cycloaddition reaction of such electron-deficient dienes with fullerenes resulted in the formation of highly functionalized bicyclo [2.2.2] octenone-fused fullerenes. The reactants were generated in situ by the oxidation of the readily available 2-methoxy phenols with hypervalent iodine agents. For the several different masked ortho-benzoquinones that were tested, it was found that the yield of the cycloadducts depends on the nature of the starting materials and the reaction conditions. Other Diels-Alder reactions of such electron-deficient dienes with electron-poor fullerenes involved tropones [94], 1,3-butadienes substituted with electron-withdrawing groups [95], and 2-pyrone [96]. 

Repetitive Diels-Alder reactions utilizing bis-ort/io-quinodimethane units have been employed[14bl for the construction of polymeric and oligomeric [60]-fullerenes with molecular weights up to 80,000 amu. The potential of using this method for dendrimer construction was suggested. 

Far more attempts have been undertaken to covalently assemble multicomponent structures with at least one Pc moiety, which will be briefly described thereafter. In particular the C6o fullerene has been connected to the Pc by using different methodologies. Besides the Pc-C6o dyads presented above, the Pc scaffold has also been covalently connected through employment of Diels-Alder reaction onto the... 

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