Anthracene adduct with maleic anhydride

In contrast to the adducts of many dienes with maleic anhydride, the above adducts are characteristically stable to heat some do not dissociate at temperatures as high as 300°. This property is apparently associated with the sulfone group, since reduction of the anthracene adduct (346) with lithium aluminum hydride affords the corresponding cyclic sulfide, which readily dissociates at 250° to give anthracene and benzo[6]thiophene.726... 

Diethyl methylidenemalonate. This reagent (3) polymerizes easily and can be prepared by depolymerization of oligomers, but is more readily available in sufficiently pure form from diethyl malonate (1) by conversion to the Diels-Alder adduct 2 from anthracene, paraformaldehyde, and 1. When heated at 190-200° with maleic anhydride, the adduct 2 decomposes to 3 in an overall yield of -50%. 

As the focus of this chapter is on the synthetic utility of the rDA reaction, an overview of mechanism is beyond the scope of this review however, the subject has beoi reviewed previously. Structural and medium effects on the rate of the rDA reaction are of prime importance to their synthetic utility, and therefore warrant discussion here. A study of steric effects cm the rate of cycloreversicHi was the focus of early work by Bachmann and later by Vaughan. The effect of both diene and dioiophile substituticHi on Ae rate of the rDA reaction in anthracene cycloadducts has been reported in a study employing 45 different adducts. If both cycloaddition and cycloreversion processes are fast on the time scde of a given experiment, reversibility in the DA reaction is observed. Reversible cycloaddition reactions involving anthracenes, furans, fulvenes and cyclopentadienes are known. Herndon has shown that the well-known exception to the endo rule in tiie DA reaction of furan with maleic anhydride (equation 2) occurs not because exo addition is faster than endo addition (it is not), but because cycloreversion of the endo adduct is about 10 000 times faster than that of the exo adduct. ... 

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. 

Dlels-Alder reaction. NAFION catalysis allows the Dlels-Alder reaction to be run at a lower reaction temperature. Reactions of anthracene with maleic anhydride, p-benzoqulnone, dimethyl maleate, and dimethyl fumarate were carried out at 60-80 C In either refluxing CHCl- or benzene. Table XVI gives % yield of the various adducts (58). 

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

Other methods for the synthesis of cyanoacrylate monomers include pyrolysis of 3-alkoxy-2-cyanopropionates (1), transesterification of cyanoacrylates with alcohols (19,20), displacement of monomer from the corresponding anthracene Diels-Alder adduct by treatment with maleic anhydride (7,21), esterification of cyanoacrylic acid or cyanoacryloyl chloride with alcohols (22), and the oxidation of alkyl 2-cyanopropionate phenyl selenides with hydrogen peroxide (23). These alternative methods are particularly useful for the preparation of monomers not readily prepared by thermal decomposition of cyanoacrylate polymer. 

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. 

Anthracene and maleic anhydride. In a 50 ml. round-bottomed flask fitted with a reflux condenser, place 2 0 g. of pure anthracene, I 1 g. of maleic anhydride (Section 111,93) and 25 ml. of dry xylene. Boil the mixture under reflux for 20 minutes with frequent shaking during the first 10 minutes. Allow to cool somewhat, add 0 5 g. of decolourising carbon and boil for a further 5 minutes. Filter the hot solution through a small, preheated Buchner funnel. Collect the solid which separates upon coohng by suction filtration, and dry it in a vacuum desiccator containing paraffin wax shavings (to absorb traces of xylene). The yield of adduct (colourless crystals), m.p. 262-263° (decomp.), is 2-2 g. Place the product (9 10-dihydroanthracene-9 10-cndo-ap-succinic anhydride) in a weU-stoppered tube, since exposure to air tends to cause hydration of the anhydride portion of the molecule. 

Anthracene and maleic anhydride with aluminum chloride give the adduct quantitatively in minutes. The product is recrystallized from ethyl acetate, mp 262-263°. 

An example of the equivalent (photoaddition) reaction following hetero-molecular photoassociation is provided by the photochemical addition of maleic anhydride to anthracene." Livingston and coworkers100 have shown that the anthracene triplet state is not involved in this reaction and that, in terms of Eq. (47) in the appropriate form, q%. = 0.03. However, if the excited complex XMQ formed directly by light absorption in the charge-transfer band is the reactive intermediate, this produces the adduct with a computed efficiency of 347 . 

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. 

A particularly attractive application of hydrotropy in organic synthesis arises when the product is bulkier than the reactant, with the result that it has lower solubility than the reactant in the hydrotrope solution. Consequently, it selectively precipitates out of the reaction mixture and can be easily filtered out. Then the hydrotropic solution can be recycled, thus minimizing the environmental hazards associated with waste disposal. An important example is the synthesis of Diels-Alder adducts that act as flame retardants for polymer blends and formulations. One of these is also used in the manufacture of the pesticide Endosulfan. The reaction involves a diene such as hexachloro-pentadiene or anthracene and a dienophile such as p-benzoquinone or maleic anhydride. The following typical reaction carried out by Sadvilkar (1995) gave excellent results ... 

The addition of anthracene to maleic anhydride (Fig. 11) was reported to be accelerated by sonication. From a mechanistic study in the presence of electron carriers, an electron transfer process was ruled out. These results could not be reproduced, and no difference between the sonochemical and thermal rates and yields was observed (adduct formation in 30% after 1 h, 50% after 3 h, with or without sonication). In the presence of monoelectronic oxidizers such as ferric chloride,or tris(4-bromophenyl)aminyl hexachloroantimonate (TBPA),28a,c change was noted in these figures, although the radical cation of anthracene was formed.43 This radical cation is not involved in the reaction pathway. 

In the presence of 1-5% of iron trichloride or TBPA under conventional conditions, 60-70% yields of the adduct are formed even at -50 C, in times as short as 15 min.43 Therefore, the conclusion is that, imder appropriate conditions, the anthracene radical cation is most probably on the reaction pathway, in contrast with the case of maleic anhydride cycloaddition. A coincidence seems then to exist between the possibility of a mechanism involving the diene radical cation and the presence of a sonochemical effect. 

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]). 

Maleic anhydride adducts of anthracene and cyclopentadiene (Fig. 4) were used in the synthesis of UPRs and apphed directly during the polycondensation reaction of maleic anhydride with ethylene glycol or diethylene glycol (Table 7) [17]. 

Fig. 4 Synthesis of maleic anhydride adducts of cyclopentadiene and anthracene. Reprinted from (1995) Polimery 40 624 [17] with permission...

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