Diels-Alder reactions of anthracenes

The synthesis of bisantrene begins with Diels-Alder reaction of anthracene (52) and ethylene... 

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. 

Table 6.2 Sodium and guanidinium salt effects (relative reaction rates) of Diels-Alder reaction of anthracene-9-carbinol and N-ethylmaleimide...

Scheme 4.3 Diels—Alder reaction of anthracene with diethyl fumarate.

Similarly, the use of a higher input power in retro-Diels-Alder reactions of anthracene derivatives has been reported to afford complete reaction in 3-5 min [36], This method is an alternative to the use of flash thermolysis. The use of graphite is a prerequisite for obtaining high temperatures in a short time. 

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). 

TABLE 3. Rate constants for the Diels-Alder reaction of anthracene and iV-ethylinaleiniide in different solvents... 

The synthesis of bisantrene begins with Diels-Alder reaction of anthracene (52) and ethylene carbonate (53) to produce adduct 54. Hydrolysis and glycol cleavage lead to bls-carboxaldehyde 55. This readily forms a bis-hydrazone with guanylhydrazine [16]. 

The isopropylation of anthracene gave similar results to that of naphthalene.84 The selectivities for 2-isopropylanthracene (2-IPA) and 2,6-diisopropylanthra-cene (2,6-DIP A) over HM(25) were as high as 91% and 47%, respectively. On the other hand, the selectivities over HY were as low as 59% and 8% for both products. The Diels-Alder reaction of anthracene with propylene occurred at higher temperatures to yield large amounts of the adducts such as 11 -methyl-9, lO-dihydro-etano-anthracene. However, their formation was prevented by the addition of a small quantity of water. 

Diels-Alder reactions.1 A key step in a synthesis of 4-demethoxydaunomy-cinone (5) involves a regioselective Diels-Alder reaction of anthracene-1,4,9,10-tetrone (2) with (1) to give the desired adduct (3) in 79% yield. A similar reaction with 2-acetoxy-1,3-butadiene affords only a 58% yield of the corresponding adduct. The product (rather unstable) is aromatized and hydrolyzed to give 4 in high yield. 

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... 

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

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... 

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

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... 

A chiral C2-symmetric bridged ferrocene was constructed from a synthetic ligand containing two cyclopentadiene units (Fig. 4-12d). The key step in the synthesis of the ligand is a diastereoselective Diels — Alder reaction of anthracene with bis[(S)-l-ethoxycarbonylethyl]fumarate. When oxidized to the ferrocinium salt, the ferrocene derivative has Lewis acid properties and catalyzes Diels — Alder reactions with some enantioselectivity [85]. 

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... 

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. 

A chiral diol was obtained from the asymmetric Diels-Alder reaction of anthracene with dimen-thyl fumarate (see Section 3.5.1. for the dienophile) in 99% ee (for details on this reaction, see ref 17). Conversion of the diol to the crown ether 13 was achieved with pentaethyleneglycol ditosylate and potassium hydroxide18. As for the other crown ethers discussed here, the compound has been used as a catalyst in enantioselective Michael additions (Section D. 1.5.2.1.). 

Compound 2 was chosen as a direct precursor to cyclo-Ci since it should lose three anthracene molecules in a retro-Diels-Alder reaction under thermal conditions (Scheme 13-1). The synthesis of 2 (Scheme 13-2) started with the Diels-Alder reaction of anthracene and tra 5-dichloroethene [10], followed by dehydrochlorination and subsequently bromination to 10. The latter conversion was best achieved by simply adding elemental bromine to a solution of the vinyl anion formed with n-BuLi [11]. Palladium-catalyzed alkynylation of 10 with trimethylsilylacetylene in n-butylamine followed by deprotection with aqueous KOH in MeOH gave the diethynyl derivative 11 as very unstable crystals, which in one case exploded spontaneously. 

Direct and reverse Diels-Alder reactions of anthracene and 9,10-dimethylanthracene with TCNE in several solvents have been investigated by measuring kinetic and thermodynamic parameters". 2-Vinylindoles 384 yielded tetrahydrocarbazoles 385 by [4+2]... 

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%). 

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