Fullerenes cycloaddition reactions

Fullerenes Cycloaddition reactions are very popular for functionalization of fullerenes. Such reactions of fullerenes are compiled and discussed in detail in Reference 253. During the last 10 to 15 years, several communications appeared concerning [3 + 2] cycloaddition of nitrile oxides to fullerene C60- Nitrile oxides, generated in the presence of C60, form products of 1,3-cycloaddition, fullerene isoxazolines, for example, 89. The products were isolated by gel permeation chromatography and appear by and 13 C NMR spectroscopy to be single isomers. Yields of purified products are ca 30%. On the basis of 13C NMR, structures with Cs symmetry are proposed. These products result from addition of the nitrile oxide across a 6,6 ring fusion (254). 

In 1995, Boyd and co-workers <95TL7971 > covalently linked a porphyrin to fullerene Cgo through a 1,3-dipolar cycloaddition reaction involving the porphyrinic azomethine ylide 28 (Scheme 8). The ylide was generated in situ from befa-formyl-meso-tetraphenylporphyrin 27 and A -methylglycine, and provided the porphyrin-C6o diad 29 in good yield. 

H. Isobe, K. Cho, N. Solin, D. B. Werz, P. H. Seeberger, and E. Nakamura, Synthesis of fullerene glycoconjugates via a copper-catalyzed Huisgen cycloaddition reaction, Org. Lett., 9 (2007) 4611-4614. 

The covalent methods previously discussed for fullerene modification using cycloaddition reactions also can be applied to carbon nanotubes. This strategy results in chemically linking molecules to the graphene rings on the outer surface of the cylinder, resulting in stable... 

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. 

Daub and colleagues have also described the cycloaddition reaction of 534 with [60]full-erene (209) (equation 157)319 and [70]fullerene320, which were the first [8 + 2] cycloaddition reactions with fullerenes described in the literature. Reaction with [60]fullerene afforded 546 as the main product with a yield of more than 90%. On the basis of the results of previous cycloadditions performed with fullerenes, it was assumed that it was a 6,6-double bond which had reacted with 533, [60]fullerene adding to the less hindered site of 534. 

The reactions described in the previous section are assumed to proceed with one-electron transfer as a key step. On the other hand, [4+2] cycloaddition reactions, which should proceed in a concerted manner in solution, were also found to proceed efficiently for fullerene Cgo under the HSVM solid-state reaction conditions. 

In cycloaddition reactions the [6,6] double bonds of Cjq exhibit a dienophilic character. A large variety of cycloadditions have carried out with Cjq and the complete characterization of the products, mainly monoadducts, has greatly increased our knowledge of fullerene chemistry. These chemical transformations also provide a powerful tool for the functionalization of the fullerene sphere. Almost any functional group can be covalently linked to Cjq by the cycloaddition of suitable addends. Some types of cycloadducts exhibit a remarkable stability for example, they can be thermally treated up to 400 °C without decomposition. This is an important requirement for further side-chain chemistry as well as for possible applications of the new fullerene derivatives, which may be of interest due to their biological activity or as new materials. 

Irradiation of 2,3-diphenyl-2//-azitine in the presence of Cgo fullerene leads to the formation of mono- and ohgo adducts (98,99). A monoadduct, l,9-(3,4-dihydro-2,5-diphenyl-2//-pytTolo)fullerene-60 was isolated and characterized. Mechanistic studies showed that under conditions of direct irradiation it was formed by a classic nitrile yhde cycloaddition but in the presence of 1,4-napthalenedicarbonitrile (DCA) it resulted from reaction of the radical cation intermediate 108. Cycloaddition reactions have also been carried out with diaza-phospholes and diazaarsoles (100) to give adducts of the type 189 (A=As,P) and with cyanogen to give 190 and with atyldiazocyanides where addition to both the azo moiety and the cyano group were observed (101). 

Kato et al. (119) explored reactions of fulvenes with a variety of mesoionic heterocycles. Unfortunately, reactions of miinchnone 38 with several fulvenes afforded complex mixtures in each case, and no identifiable products were reported, although Friedrichsen and co-workers (120-122) previously reported the reaction between mtinchnones and fulvenes to give cycloadducts. Kato et al. (123) also studied the cycloaddition reactions of tropone with several mesoionic heterocycles. Despite heroic efforts, the reaction of tropone with miinchnone 38 was complex and could not be unraveled. However, as described later, the reaction of tropone with isomtlnchnones was successful. Wu et al. (124) effected the cycloaddition between a miinchnone and fullerene-60 (Ceo) to give the corresponding dihydropyrrole in excellent yield. 

Among the reactions applied in the synthesis of fullerene derivatives cycloaddition reactions such as [2 + 1]-, [2 + 2]-, [3 + 2] and [4 + 2] cycloadditions play a dominant role. In these reactions ring-fused fullerene derivatives are obtained, at least with incorporation of heteroatoms such as oxygen, nitrogen, or silicon. In this section photochemical reactions leading to cycloalkyl ring-fused fullerene adducts will be presented. Photocycloaddition reactions leading to C6o-fused heterocycles will be discussed later. 

Secondary Functionalization of Fullerene Monoadducts by Cycloaddition Reactions... 

The dihydrothiopyran unit has been fused onto [60]fullerene through reaction with a thioacrylamide and an acyl chloride (95CC565). Cycloadditions also feature in the synthesis of... 

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]. 

Some novel C60-based assemblies were recently synthesized by [4+2] Diels-Alder cycloaddition reactions. Thus, fused tetrathiafulvalene-C60 dyads and C60-tetra-thiafulvalene-C60 dumbbell triads, in which the fullerene acceptor is doubly tethered to the donor tetrathiafulvalene through a rigidified cyclohexene ring [108], were prepared. With this novel approach, control of the relative orientation as well as the distance between the donor and acceptor units was achieved. Thereby, through-space interactions were expected to dominate because of the special topology of the constructed molecules. More examples of such donor-acceptor hybrid systems are discussed in the appropriate following sections, with their potential use in innovative technological applications. 

Several organofullerene donor-acceptor molecular material hybrid systems have been synthesized via 1,3-dipolar cycloaddition reactions of azomethine ylides, via Bingel cyclopropanation and methanofullerene formation intermediates as well as via cycloaddition reactions, that have already been discussed in previous sections. The majority of such hybrid systems possess always as acceptor unit the fullerene core and as donor moieties porphyrins, tetrathiafulvalenes, ferrocenes, quinones, or electron-rich aromatic compounds that absorb visible light [190-193]. The most active research topic in this particularly technological field relies (i) on the arrangement of several redox-active building blocks in... 

In 2002, a triad molecule including dithienylethene (DTE), porphyrin (P), and fullerene (DTE-P-C60) was first designed and synthesized as a photoinduced electron transfer (PET) switch by D. Gust et al. [33], as shown in Scheme 5. This molecule was synthesized by modified procedures reported literature Porphyrin chromophore was covalently linked to substituted dithienylethene by Sonogashira coupling reaction. Fullerene was introduced by the cycloaddition reaction of dyad aldehyde (dithienylethene-porphyrin aldehyde) with the fullerene and the N-methyl-glycine. 

It is clear that at the single-dimer site, the most stable adsorption configuration is S . The chemisorption process takes advantage of two cycloaddition reactions to support the adhesion of fullerene on the c(4 x 4) reconstructed GaAs(OOl) surface. Nevertheless, due to the initial structural alignment prior to the energy minimization,... 

---