Diels-Alder reactions anthracene + maleic anhydride

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... 

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. 

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. 

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. ... 

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-... 

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 is a purely cis-addition the relative positions of the substituents are retained in the adduct (compare anthracene and maleic anhydride above). ... 

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 benzyne functions as a dienophile towards reactive diene systems. The reactivity of the 9,10-positions in anthracene is well known (Diels-Alder reaction, Section 7.6), and addition of benzyne to 9-bromoanthracene yields the interesting cage-ring alkyl halide 9-bromotriptycene (9-bromo-9,10-o-benzenoanthracene). The reaction is incomplete and some unreacted 9-bromoanthracene remains in the crude reaction products, but may be removed by virtue of its ready conversion into a maleic anhydride adduct in a further Diels-Alder-type reaction. 

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

Simons, J. P. The influence of light on the Diels-Alder-reaction between anthracene and maleic anhydride. Trans. Faraday Soc. 56, 391 (1960). 

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]. 

Microwave-assisted Diels-Alder reaction of anthracene and maleic anhydride (p. 85)... 

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. 

In 1960, Yates and Eaton reported that an approximate rate acceleration of 10 was observed for the Diels-Alder reaction of anthracene and maleic anhydride in the presence of aluminum chloride (Scheme 1) [8]. This finding had important practical ramifications since it demonstrated that the Diels-Alder reaction could be conducted under mild conditions when an electropositive metal was used to lower the energy of activation. 

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