Diels-Alder reaction anthracene with maleic anhydride

The discovery that Lewis acids can promote Diels-Alder reactions has become a powerful tool in synthetic organic chemistry. Yates and Eaton [4] first reported the remarkable acceleration of the reactions of anthracene with maleic anhydride, 1,4-benzoquinone and dimethyl fumarate catalyzed by aluminum chloride. The presence of the Lewis-acid catalyst allows the cycloadditions to be carried out under mild conditions, reactions with low reactive dienes and dienophiles are made possible, and the stereoselectivity, regioselectivity and site selectivity of the cycloaddition reaction can be modified [5]. Consequently, increasing attention has been given to these catalysts in order to develop new regio- and stereoselective synthetic routes based on the Diels-Alder reaction. 

Luche and coworkers [34] investigated the mechanistic aspects of Diels-Alder reactions of anthracene with either 1,4-benzoquinone or maleic anhydride. The cycloaddition of anthracene with maleic anhydride in DCM is slow under US irradiation in the presence or absence of 5% tris (p-bromophenyl) aminium hexachloroantimonate (the classical Bauld monoelectronic oxidant, TBPA), whereas the Diels Alder reaction of 1,4-benzoquinone with anthracene in DCM under US irradiation at 80 °C is slow in the absence of 5 % TBPA but proceeds very quickly and with high yield at 25 °C in the presence of TBPA. This last cycloaddition is also strongly accelerated when carried out under stirring solely at 0°C with 1% FeCh. The US-promoted Diels Alder reaction in the presence of TBPA has been justified by hypothesizing a mechanism via radical-cation of diene, which is operative if the electronic affinity of dienophile is not too weak. 

The single-electron transfer from one excited component to the other component acceptor, as the critical step prior to cycloaddition of photo-induced Diels Alder reactions, has been demonstrated [43] for the reaction of anthracene with maleic anhydride and various maleimides carried out in chloroform under irradiation by a medium-pressure mercury lamp (500 W). The (singlet) excited anthracene ( AN ), generated by the actinic light, is quenched by dienophile... 

The Diels-Alder reaction of benzenoid aromatic hydrocarbons with dienophiles was discovered more than fifty years ago [61, 62]. A classical example is the reaction of anthracene with maleic anhydride (Scheme 5). Although this type of reaction, termed endogenic or endocyclie Diels-Alder reaction, could be expected to be particularly well suited for correlating structure (topology) of benzenoid hydrocarbons with kinetic data, the problem has been systematically studied only very recently. Biermann and Schmidt in a series of publications [12, 29, 45, 63, 64] reported second-order rate constants (k2), measured under standard conditions (1,2,4-trichlorobenzene, 91.5 + 0.2 °C), for the endocyclie Diels-Alder reaction between maleic anhydride and 102 benzenoid hydrocarbons. Each rate constant was measured twice, the values usually... 

Scheme 5. Endocyclic Diels-Alder reaction of anthracene with maleic anhydride...

Later, Lewis acids were suggested as catalysts for Diels-Alder addi-tions in the case of the reaction of anthracene with maleic anhydride the acceleration due to AICI3 was estimated to be of the order of 10 . As has been mentioned (Section 4.1.1), in the presence of Lewis acids endo adducts are more favoured than in uncatalysed reactions, and there is more selectivity in orientation when unsymmetrical dienes and dienophiles add to each other furthermore, with an optically active reactant, asymmetric induction can be stronger in the catalysed reaction (Table 4, footnote b). it should be appreciated that substrates sensitive to AICI3 and similar catalysts are always polar molecules, usually containing carboxyl or carbonyl groups, to which Lewis acids can become bound. 

In this particular instance the Diels-Alder reaction is vividly exemplified by the tmion of anthracene with maleic anhydride to give rise to the formation of 9, 10-dihydroanthracene-9,10-encfo-aP-succinic anhydride. However, it may be observed that by virtue of this reaction both the outer rings of the anthracene nucleus have become truly aromatic in character. 

Nafion-H is an efficent catalyst for Diels-Alder reactions (Table 3.39). The reactions of anthracene with maleic anhydride, dimethyl maleate, and dimethyl fuma late were carried out at 333 — 353 K in the presence of Nafion-H catalyst in either chloroform or benzene solvent. It should be noted that the reaction of dienophiles with very reactive dienes such as isoprene and 2,3-dimethylbutadiene can be carried out at room temperature to give the adduct in hi( yields. In usual systems, highly reactive dienophiles undergo polymerization during the desired reactions. In Diels-Alder reactions catalyzed by Friedel-Crafts Lewis acid catalysts, excess amounts of Lewis acid halides are required because of the formation of the complex between the halide and carbonyl oxygen atoms. Here again, Nafion-H catalysts allow easy and clean separation of products and the catalysts are not destroyed upon work up. 

Another reaction that demonstrates the similarity in energy between one anthracene and two benzene rings is the Diels-Alder reaction of anthracene with maleic anhydride... 

The thermal Diels-Alder reactions of anthracene with electron-poor olefinic acceptors such as tetracyanoethylene, maleic anhydride, maleimides, etc. have been studied extensively. It is noteworthy that these reactions are often accelerated in the presence of light. Since photoinduced [4 + 2] cycloadditions are symmetry-forbidden according to the Woodward-Hoffman rules, an electron-transfer mechanism has been suggested to reconcile experiment and theory.212 For example, photocycloaddition of anthracene to maleic anhydride and various maleimides occurs in high yield (> 90%) under conditions in which the thermal reaction is completely suppressed (equation 75). 

Olah et al.902 demonstrated in 1979 that Nafion-H is able to catalyze Diels-Alder reaction of anthracene with a number of dienophile (maleic anhydride [Eq. (5.329)], para-benzoquinone, dimethyl maleate, dimethyl fumarate) in chloroform or benzene... 

The Diels-Alder reaction is a well-established synthetic method that allows the creation of two new carbon-carbon bonds and leads to the formation of six-membered rings. Eventually, the photochemical reaction can advantageously compete with the thermal process. For instance, anthracene undergoes thermal and photochemical Diels-Alder reactions with alkenes, but the photoinduced addition of maleic anhydride to the homochiral anthracene, as depicted in Scheme 9.28, is faster than the thermal reaction and occurs with excellent diastereoselectivity (only one diastereoisomer) [42]. 

The dienic character of the central ring is illustrated by the reaction of anthracene with dienophiles in Diels-Alder reactions. For example, c -butenedioic anhydride (maleic anhydride) reacts readily when benzyne is generated in the presence of anthracene, triptycene (19) is produced. 

The studies reported last year on the stereoisomeric control of the photo-induced Diels Alder reaction of maleic anhydride with homo-chiral anthracene derivatives such as (46) have been extended using 320-400 nm radiation, and this gives the head-to-tail anthracene dimer as well as the previously reported adduct (47) with excellent diastereoselectivity. The thermal and photochemical retroaddition process has been examined and the results suggest that this facile process may promote the anthracene as a new chiral auxiliary. 

Most of the classical dienes are hydrocarbons, like cyclopentadiene. butadiene, anthracene, 9,10-dimethylanthracene, isoprene, 2,3-dimethylbutadiene. For dienes of this kind it is generally true that electrophilic dienophiles are the most reactive, and actually acrylic derivatives, maleic anhydride, p-benzo-quinone and similar compounds have found a large use as dienophiles both for preparative purposes and for kinetic studies. The latter demonstrated quantitatively the importance of electronegative groups on the dienophiles, and conversely of electron-releasing substituents on the diene, in order to accelerate such type of Diels-Alder reaction. It was also realised later that Diels-Alder additions with inverse electron demand , that is between electrophilic dienes and nucleophilic dienophiles, do occur . ... 

An exception, with respect to the photosensitised reactions mentioned so far, is represented by the Diels-Alder addition of maleic anhydride to anthracene in dioxane, carried out under irradiation ( = 365 nm) without sensitisers, at 26-45°C. The rate of removal of anthracene was found to be linearly dependent on the total light absorption. As maleic anhydride quenches the fluorescence (transition from excited singlet to ground state) of anthracene, and in agreement with the kinetic evidence, a mechanism was suggested by which singlet anthracene is responsible for cycloaddition rather than triplet anthracene. According to this mechanism, the reaction of the excited diene with maleic anhydride has a rate coefficient of about 3x 10 l.mole . sec, i.e. of the same order as the reported frequency factor of the thermal reac-... 

Anthracene undergoes a Diels-Alder reaction with maleic anhydride to give a cycloadduct with the formula C18H12O3. What is its structure ... 

Anthracene can be separated from the other polycyclics by adduct formation (Diels-Alder reaction) with maleic anhydride. 

This experiment is a further example of the Diels-Alder reaction. For a discussion of the basic aspects of this reaction see Experiment [14]. In the present case, the central ring of anthracene is shown to possess the characteristic properties of a diene system. Thus, this aromatic compound reacts to form stable Diels-Alder adducts with many dienophiles at the 9 and 10 positions (the two positions on the central ring where new bonds can be made without destroying the aromaticity of the other two rings). Maleic anhydride, a very reactive dienophile, is used here in the reaction with anthracene. Note, that as this reaction is reversible, it is usually best carried out at the lowest possible temperatures consistent with an acceptable reaction rate (see Experiment [14]). 

Higher molecrolar weight polynuclear aromatic hydrocarbons (PAHs) containing the anthracene nucleus have also been found to react with maleic anhydride. These ring systems, however, can differ widely in reaction rates. Typical examples of those systems that undergo the Diels-Alder reaction are 1,2,5,6-dibenzanthracene (a), 2,3,6,7-dibenzanthracene (pentacene) (b), and 9,10-diphenylanthracene (c). 

Finally, extended arenes such as anthracene (C14H10) undergo other cycloaddition reactions. Thus, as shown in Equation 6.90, anthracene (CwHio) undergoes a thermally allowed [4 + 2] cycloaddition (Diels-Alder) reaction with dienophiles such as Z- or dx-butenedioic anhydride (maleic anhydride, C4H2O3) and a photochemically allowed [4 -1- 4] cycloaddition reaction with itself (Equation 6.91). 

PROBLEM 13.59 Even though naphthalene and anthracene are polynuclear aromatic compounds, they undergo the Diels-Alder reaction. For example, anthracene readily reacts with maleic anhydride. However, the reaction of naphthalene with maleic anhydride proceeds efficiently only under high pressure. 

Doping of the liquid crystals with carbazole was limited by the solubility of carbazole, i.e. about 10" m. Colourful microcrystals could easily be observed when the solubility was exceeded by viewing the oriented samples in a polarizing microscope with the liquid crystalline phase giving a dark background. The carbazole utilized here was purified to remove anthracene by a Diels-Alder reaction with maleic anhydride. ... 

Yates reported in 1960 that the Diels-Alder reaction is highly responsive to Lewis acid catalysis. Extraordinary rate acceleration was observed for the cycloaddition of maleic anhydride with anthracene in the presence of aluminum trichloride (4 2 = 2400 hr versus 1 min Equation 1) [17]. This landmark finding initiated intense investigations that led to the development of a large number of catalysts to effect stereoselective Diels-Alder reactions. Interest-... 

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