9- anthracene, Diels-Alder cycloaddition

Kochi and co-workers engineered heteromolecular charge-transfer crystals of a tricyclic dithiin 34 stacked alternately with anthracene, which can undergo spontaneous Diels-Alder cycloaddition to give a novel artificial crystal system <2001JA87, 2001JA4951>. 

Kochi and co-workers studied photoinduced Diels-Alder cycloadditions via direct photoexcitation of anthracene as a diene with maleic anhydride and various maleimides as dienophiles. Here, fluorescence-quenching experiments, time-resolved absorption measurements, and the effect of solvent polarity provide striking evidence for an ion-radical pair to be the decisive intermediate [83],... 

Triptycene is the Diels-Alder cycloaddition product from the reaction of benzyne with anthracene (compound A). Although anthracene is aromatic, it is able to undergo cycloaddition at the center ring with a dienophile because the adduct retains the stabilization energy of two benzene rings. 

For example, the rate of the Diels-Alder cycloaddition reaction between 9-(hydroxymethyl)anthracene and A-ethylmaleimide, as shown in Eq. (5-159), is only slightly altered on changing the solvent from dipolar acetonitrile to nonpolar isooctane, as expected for an isopolar transition state reaction cf. Section 5.3.3. In water, however. 

Naphthalene and anthracene can also be prepared via a Diels-Alder cycloaddition of a quin one with a diene,... 

Diels-Alder cycloadditions involving thiete sulfones as dienophiles occur with butadiene,cyclopentadiene, 1,2,3,4-tetraphenylcyclopentadiene, anthracene. tetraphenylcyclopentadienone, l,3-diphenyl-2H-cyclopenta[l]-phen-anthrene-2-one, a-pyrone, l-(Af,Af-dimethyl)- and l-(7V,A -diethyl)-l,3-butadiene, furan, 2,5-dimethylfuran, l,3-diphenylisobenzofuran, isobenzofuran," and l,3-diphenylnaphtho[2,3-c]furan. Generally, thiete... 

A method has been developed that combines the advantages of solid-supported catalyst extraction and solution-phase reactivity. By preparing a palladium complex bearing an anthracene tag, this can then be attached to a solid support via a chemoselective Diels-Alder cycloaddition to sequester the palladium catalyst along with any dissociated phosphine or phosphine oxide at the end of the reaction, leaving the desired catalysis product in the solution. The basis of the methodology is shown in Scheme 15. 

The butadienylphosphonium salts (120) are formed in the reactions of phosphines with alkenoyl bromides. Diels-Alder cycloaddition reactions of vinyltriphenylphosphonium bromide with cyclopentadiene and anthracene derivatives have been used (together with conventional quaternization procedures)... 

Scheme 8-18 Template synthesis via double Diels-Alder cycloaddition of anthracene endcaps to norbomadiene oligomers.

In the mid-1980s, Hoffman and co-workers described a simple synthesis of racemic mikanecic acid via in situ Diels-Alder dimerization of the diene generated from t-butyl 2-bromomethylbut-2-enoate. " The first example of a Diels-Alder reaction of a MBH adduct was the dimerization of 2-hydroxy-alkyle-nones" and the previously mentioned addition to anthracene. The appKcation of the MBH adducts as hetero dienes or precursors of dienes, and dienophiles for the Diels-Alder cycloaddition reactions was then initiated and expanded by the group of Hoffman. In a series of reports, Hofftnan and co-workers have described the in situ Diels-Alder dimerization of various dienes (157), generated via stereoselective dehydration with MsCl-DABCO-DMAP of the corresponding MBH adducts The elimination of water from MBH adducts always resulted... 

Nonracemic a,P-unsaturated p-tolylsulfoxide dienophiles bearing an electron-withdrawing group in the a-position have been employed successfully in Diels-Alder cycloadditions [28,29,94,133], although less frequently than their 3-substituted counterparts. Koizumi and coworkers have reported the use of optically active 2-p-tolylsulfinylacrylate (188) as a chiral dienophile which exhibits high reactivity and diastereoselectivity in cycloaddition reactions with anthracene and cyclopentadiene (Scheme 5.62), affording cycloadducts (189) and (190),... 

Molecular dynamic simulations show that the confined space of SWCNTs may influence both the kinetics and thermodynamics of the Diels-Alder reactions between anthracenes and N-substituted maleimide guests, favoring an unusual regioselectivity. Thus, in the confined space of CNTs, the 1,4-exo adduct of a Diels-Alder cycloaddition may be produced instead of the 9,10-adduct, which is favored in bulk. It is possible that the nanotube chirality could influence the outcome of the reaction, as this could alter the preferred orientation of the reactants inside the SWCNT. However, it was snspected that the diameter of the SWCNT is likely to have by far the largest influence on the reaction outcome, as this will have the biggest influence on how close the reactants can approach each other [195]. 

During their studies on Diels-Alder cycloaddition, Kotsuki s group has developed the synthesis of a new class of anthracene-fused proline catalysts. Among them, the amino acid (5)-27 resulted to be the most efficient when the... 

Diels-Alderase ribozymes (DAR), isolated from a combinatorial RNA library, cause a (2 X 10 )-fold acceleration of the Diels-Alder cycloaddition of anthracene covalently tethered to ribozyme and a biotinylated maleimide in aqueous-buffered medium (Scheme 5.15). Jaschke recently reported the action of Diels-Alderase ribozymes as true catalysts, in the sense that they catalyze the cycloaddition of anthracene that is not covalently tethered to RNA and biotin maleimide in aqueous-buffered medium. 

The same group also reported on the synthesis of multiarm star block copolymers by using Diels-Alder cycloaddition reactions (Dag et al., 2009). First, an a-anthracene-end functionalized PS (PS-anthr) and furan-protected maleimide-end-functionaUzed polymers, including PMMA and PtBuA, were prepared via ATRP. The maleimide functionalities were protected as they can contribute to the copolymerization with MMA or tBuA. Moreover, the polymerization temperature was kept below 60 °C to prevent deprotection during the polymerization. In the next step, a 33-arm anthracene-end functionalized (PS) star polymer was obtained using PS-anthr as macroinitiator and divinyl benzene as crosslinker. These star polymers were then reacted with the unprotected maleimide end-functionalized PMMA or PtBuA to give multiarm star block copolymers via Diels-Alder click reaction. The efficiencies were foimd to be 96 and 88%, respectively. 

This result proves that well-defined structures with low degree of heterogeneity of the multiarm star-shaped polymers can be synthesized. Moreover, the method reported herein can also provide a synthetic pathway for the introduction of block copolymers synthesized via different polymerization routes (RAFT, ROP, etc.) onto the anthracene-end-functionalized multiarm star-shaped polymers. Although the Diels-Alder cycloaddition between anthracene and maleimide derivatives has proven to provide good results in the formation of complex architectures, the major drawback of this method remains the requirement of high temperature and relatively long reaction times. 

Garrigues et al. (1996) reported the microwave-assisted Diels-Alder reaction between anthracene and azadienes supported on graphite, while Diaz-Ortiz et al. (2000) studied the solvent-free microwave-assisted Diels-Alder cycloaddition reaction, where a 1,2,3-triazole ring serve as a diene towards DMAD. 

In 1997, RoteUo and Nie prepared a thermoreversible main-chain C< -polymer, introducing a poly-Diels-Alder cycloaddition strategy [llaj. They reacted [tiOjfuller-ene with bis-anthracene derivative 3 in a 1 1 molar ratio at room temperature, obtaining polymer 4 in moderate yield (Scheme 2.2). 

Bis(trifluoromethyl)-l,l-dicyanoethylene is a very reactive dienophile. It undergoes facile and high-yield [2+4] cycloadditions with 1,3-dienes, cyclopen-tadiene, and anthracene [707] (equation 86). It is reactive enough in a Diels-Alder reaction with styrene [702] (equation 86). 

For a recent discussion on the stereochemical aspects of the Diels-Alder reaction with vinyl sulphoxides see References 662, 663. It should be pointed out that vinyl sulphoxides can be considered in [2 + 4]-cycloadditions as acetylene synthons since the sulphinyl moiety may be removed from the product by sulphenic acid elimination. Paquette and coworkers took advantage of this fact in the synthesis of properly substituted anthracenes 562664, (equation 360). 

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... 

Rideout and Breslow first reported [2a] the kinetic data for the accelerating effect of water, for the Diels Alder reactions of cyclopentadiene with methyl vinyl ketone and acrylonitrile and the cycloaddition of anthracene-9-carbinol with N-ethylmaleimide, giving impetus to research in this area (Table 6.1). The reaction in water is 28 to 740 times faster than in the apolar hydrocarbon isooctane. By adding lithium chloride (salting-out agent) the reaction rate increases 2.5 times further, while the presence of guanidinium chloride decreases it. The authors suggested that this exceptional effect of water is the result of a combination of two factors the polarity of the medium and the... 

An example of a /zctcro-Diels-Alder reaction in SC-CO2 is the cycloaddition of anthracene with 4-phenyl-1,2,4-triazoline-3,5-dione, carried out at 40 °C and at a pressures between 75 and 216 bar [86]. The rate constant increases with decreasing pressure and the highest reactivity was observed at the critical pressure. The value of the rate constant at the critical pressure was higher than that observed in liquid CHCI3 and MeCN at the same temperature. At higher pressures, the rate is slower than that in the polar solvents, which reflects the apolar nature of SC-CO2 as a solvent. 

The study of the cycloaddition behavior of l,l-dichloro-2-neopentylsilene, C Si =CHCH2Bu (2) [3], reveals the high polarity of the Si=C bond and a strong electrophilicity. The [4+2] cycloaddition reactions with anthracene (3), cyclopentadiene (4) and fulvenes (5) proceed as expected surprising, however, the Diels-Alder reactions with dienes are of lower activity, like naphthalene (6) and furans (7). 

Methods have been described that involve microwave-assisted graphite-supported dry media for the cycloaddition of anthracene, 1-azadienes and 1,2,4,5-tetrazines with several C-C dienophiles and carbonyl compounds in hetero-Diels-Alder reactions [35], This technique leads to a shortening of reaction times, a situation that enables work to be undertaken at ambient pressure in an open reactor to avoid the formation of unwanted compounds by thermal decomposition of reagents or products. 

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). 

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