9-Substituted anthracenes Diels-Alder reactions

Breslow studied the dimerisation of cyclopentadiene and the reaction between substituted maleimides and 9-(hydroxymethyl)anthracene in alcohol-water mixtures. He successfully correlated the rate constant with the solubility of the starting materials for each Diels-Alder reaction. From these relations he estimated the change in solvent accessible surface between initial state and activated complex " . Again, Breslow completely neglects hydrogen bonding interactions, but since he only studied alcohol-water mixtures, the enforced hydrophobic interactions will dominate the behaviour. Recently, also Diels-Alder reactions in dilute salt solutions in aqueous ethanol have been studied and minor rate increases have been observed Lubineau has demonstrated that addition of sugars can induce an extra acceleration of the aqueous Diels-Alder reaction . Also the effect of surfactants on Diels-Alder reactions has been studied. This topic will be extensively reviewed in Chapter 4. 

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 scope of the microwave technique in the preparation of fullerene derivatives was determined in the well known Diels-Alder reaction of C6o with anthracene (1) [71], which has been reported to occur under thermal conditions (13% [71a], reflux, toluene, three days 25% [71b], reflux, benzene, 12 h) (Scheme 9.22). In addition to 76, multiply-substituted adducts that undergo cycloreversion to the starting materials were formed. 

Microwave-assisted Diels-Alder reactions of 9-substituted anthracenes with 2-acetamidoacrylate in DMF generate conformationally constrained bicyclic bisaryl a-amino acid derivatives with high regioselectivity.138 The Sc(OTf)3-catalysed Diels-Alder reaction of anthracenes with methyl vinyl ketone does not proceed via an electron-transfer process from anthracenes to the MVK-Sc(OTf)3 complex.139 (-)-(/ )-9-(l,2-Dimethoxyethyl)anthracene has been used as a chiral template in the Diels-Alder/retro-Diels-Alder sequence for the synthesis of a,j3-unsaturated lactams.140... 

It is important to emphasize that three different types of reactions, i.e., electron transfer from (TPP)Co to Q (Eq. 13), Diels-Alder reaction of anthracenes with Q (Scheme 12) and hydride transfer from BNAH to Q (Scheme 14), have the common rate-determining step of Mg +-catalyzed electron transfer from these electron donors to Q. In each case, the relative catalytic dependence of A obs on [Mg ] is the same as indicated by Eq. 14, irrespective of different electron donors. The nucleophilic addition of a / ,/ -dimethyl-substituted ketene silyl acetal such as Me2C= C(OMe)OSiMe3 is also catalyzed by Mg + in MeCN [227, 228]. No reaction takes... 

Site selectivity is that selectivity shown by a reagent towards one site (or more) of a polyfunctional molecule, when several sites are, in principle, available. The preference for electrophilic attack at the ortho and para positions of X-substituted benzenes is just one of many examples discussed in Chapter 3. In cycloadditions, site selectivity always involves a pair of sites thus, butadiene reacts faster with the quinone (308) at C-2 and C-3 than at C-5 and C-6,256 and Diels-Alder reactions of anthracene (309) generally take place257 across the... 

Wang and co-workers also evaluated the reactivity of 9-substituted anthracene in Diels-Alder reactions with fullerene. Corresponding adducts were prepared in high yields under solvent-free conditions using the high-speed vibration milling technique (Scheme 8.14). ... 

Scheme 8.14 Diels-Alder reactions of fullerene with a 9-substituted anthracene.

The photochemical Diels-Alder reactions of anthracene with fumarodinitrile and 1,4-benzoquinone have been studied in chloroform solution. Not surprisingly, the addition occurs in competition with dimerization of the arene and proceeds by way of electron transfer from anthracene to the dienophiles. The radical ion pair has been detected by transient absorption spectroscopy, and the resulting diradical precursor of adduct formation from the quinone was observed by ESR at 77 K. 2,7-Dibromotropone is reported to undergo (871+471) photoaddition to 9,10-dicyanoanthracene in benzene-methanol (9 1), giving (25) as the primary adduct which is then proposed to react with methanol and water (solvent contaminant) to yield the final product (26). In contrast, 2-bromotropone and the anthracene in CH2CI2 solution afford the substitution products (27) (62%) and (28) (25%). 

Wang GW, Chen Z-X, Murata Y, Komatsu K. [60]Fullerene adducts with 9-substituted anthracenes mechanochemical preparation and retro Diels-Alder reaction. Tetrahedron 2005 61 4851-6. 

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]. 

Olefins of the type (177), which are readily prepared from the keten-anthracene adduct (176), undergo retro-Diels-Alder reactions to give high yields of mono- or di-substituted acetylenes. ... 

The Diels-Alder reaction ([4+2] cycloaddition) [8] provides one of the most powerful methods for the constmc-tion of PAHs because it affords one-step formation of the six-membered ring framework, the basic unit of these derivatives. This chapter, based on the results of our work, will highUght the synthesis of substituted oligoacenes including anthracene (1), tetracene (2), and pentacene (3) cores by Diels-Alder reactions using arynes and quinones as dienophile components and furans, thiophene-1,1-dioxides, and o-quinodimethane as diene components. The synthetic methodology will be accompanied by discussions on molecular and packing stmctures as weU as solid-state optical properties. 

A series of alkyl-substituted anthracenes (14,18, and 24) were prepared from Diels-Alder reactions of bis(benzyne) equivalent 4 or dehydronaphthalene equivalent 8 with alkyl-substituted furans (11 or 27). The structural features of the crystals were characterized by X-ray crystallographic analysis. Depending on the length, position, and number of alkyl side chains, the molecular structures (alkyl conformations) and packing arrangements of the alkyl-substimted anthracenes changed drastically. Consequently, such modifications led to diffaent fluorescait properties for the anthracenes in the solid-state. 

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