Diels-Alder reactions of 1,2-benzoquinones

Wassermann (6) has studied the Diels-Alder reaction of benzoquinone (B) and cyclopen-tadiene (C) at 25 °C. 

Indeed, it has been found that the Diels-Alder reaction of benzoquinone 47 and cyclohexadiene 48 is accelerated by encapsulation in the hydroxysoftball 7-7.[251 It is known that the capsule in its resting state is occupied with two benzoquinone molecules,... 

Figure 8. Catalytic cycles for the Diels-Alder reactions of benzoquinone 47 with cyclohexadiene 48 (top) and tetramethyl thiophene dioxide 51. While the reaction of 47 with 48 suffers from product inhibition, adduct 52 is easily replaced by new reactants inside the capsule.

Problem 19.29 Write a structural formula for the product of the Diels-Alder reaction of / -benzoquinone with ... 

J.D. White et al. reported the total synthesis of ( )-ibogamine via the catalytic asymmetric Diels-Alder reaction of benzoquinone. The azatricyclic framework of the molecule was established by converting the bicyclic ketone to the anti oxime and then subjecting it to a Beckmann rearrangement in the presence of p-toluenesulfonyl chloride to afford the 7-membered lactam. Elaboration of this lactam into the azatricyclic core of ibogamine and later to the natural product itself was accomplished in a few additional steps. 

White, J. D., Choi, Y. Catalyzed Asymmetric Diels-Alder Reaction of Benzoquinone. Total Synthesis of (-)-lbogamine. Org. Lett. 2000, 2, 2373-2376. 

Diels—Alder reaction of benzoquinone with an excess of anthracene furnishes the extended quinone 25 after oxidation with HO Bra. Nucleophilic addition of Li—C=C—SiMea and aqueous workup lead to a diastereomeric mixture of two diols. Tin(II) chloride conveniently deoxygenates the diols 26 to the diethyn-ylated pentypticene derivative 27 after cleavage of the trimethylsilyl groups with NaOH. It should be possible to scale-up the reaction to multigram quantities and develop diethynylpentypticene 27 into a cornerstone monomer for further PPE syntheses. 

This route, like the Diels-Alder reaction of benzoquinone with butadiene, has found no large-scale application to date. 

Another example of a Diels-Alder reaction of benzoquinone 24 with a substituted cyclopentadienone 23 is the synthesis of a molecular ribbon (Scheme 7) [26]. The compound is twisted in two directions and does not adopt a single longitudinal twist as originally intended. Again, no route for the aromatization has been described. 

The Diels-Alder reactions of dienes 11 and 12 with many dienophiles allowed other fluorinated aromatics to be synthesized [12,13]. For example, diene 11 reacted with dimethylacetylenedicarboxylate and ethylpropiolate (Scheme 2.8) to give trifluoromethyl diethylphthalate and trifluoromethylethylbenzoate, and diene 12 with/ -benzoquinone affords 5-fluoronaphthoquinone (Equation 2.5). 

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. 

Enantiomers (M)- and (P)-helicenebisquinones [32] 93 have been synthesized by high pressure Diels-Alder reaction of homochiral (+)-(2-p-tolylsulfo-nyl)-l,4-benzoquinone (94) in excess with dienes 95 and 96 prepared from the common precursor 97 (Scheme 5.9). The approach is based on the tandem [4 + 2] cycloaddition/pyrolitic sulfoxide elimination as a general one-pot strategy to enantiomerically enriched polycyclic dihydroquinones. Whereas the formation of (M)-helicene is explained by the endo approach of the arylethene toward the less encumbered face of the quinone, the formation of its enantiomeric (P)-form can be the result of an unfavourable interaction between the OMe group of approaching arylethene and the sulfinyl oxygen of 94. 

The rate of the Diels-Alder reaction betweenp-benzoquinone and cyclopenta-diene was measured in SC-CO2 and subcritical CO2 [85]. Relative reaction rates at different pressures are reported in Table 6.14. On going from CO2 in the liquid phase (below 31 °Q to SC-CO2, the reactivity increased significantly only when the reaction was carried out under high pressure. At 30 °C and 60 bar the reaction was 1.36 times faster than when it was performed in diethyl ether at 30 °C and 1 bar. 

Furukawa and coworkers reported preparation and isolation of thiophene 1-oxides 111-113. Diels-Alder reaction of 111 with maleic anhydride, benzoquinone, and cw-l,2-dibenzoylethylene gave the corresponding syn adducts exclusively [61] (Scheme 50). 

The Diels-Alder reactions of alkyl-substituted benzoquinones with penta-1,3-diene and isoprene were also studied in aqueous cyclodextrin solutions. Highly enhanced ortho- and mefa-regioselectivities were observed (Eq. 12.11).48... 

In total syntheses where a homogeneously catalyzed transfer hydrogenation is applied, almost exclusively aluminum(III) isopropoxide is utilized as the catalyst. At an early stage in the total synthesis of (-)-reserpine (65) by Woodward [106], an intermediate with two ketone groups and two C-C double bonds is formed (66) by a Diels-Alder reaction of para-benzoquinone (67) and vinylacry-late (68). The two ketone groups were reduced with aluminum(III) isopropoxide... 

Marchand and coworkers102 reported a difference in site selectivity between the thermodynamically and kinetically controlled Diels-Alder reactions of cyclopentadiene with 2,3-dicyano-p-benzoquinone (126) (equation 37). Under kinetic conditions, the more reactive double bond of 126 reacted with cyclopentadiene affording 127, whereas the less substituted double bond reacted under thermodynamic conditions affording 128. Both reactions proceeded with complete endo selectivity. These findings were in agreement with ab initio HF/3-21G calculations. 

Liao and coworkers124 studied the Diels-Alder reactions of substituted furans, now acting as dienophiles, with masked o-benzoquinones. A representative reaction has been depicted in equation 50. The masked o-benzoquinones such as 181 reacted with unactivated, electron-rich as well as electron-poor furans such as 182. The substitution pattern of the masked o-benzoquinones proved, however, more important. An electron-withdrawing... 

The asymmetric Diels-Alder cycloadditions of enantiopure (5)-5-(/ -tolylsulfinyl)-1,4-benzoquinones with Dane s diene under thermal and Lewis acid conditions produce tetracyclic quinones after spontaneous elimination of the sulfinyl group.The Diels-Alder reaction of barrelene with o-benzoquinone produces tetracyclo[6.2.2.2 .0 ]tetradeca-9,ll,13-triene-4,5-dione. Under kinetic control, the Diels-Alder cycloaddition of 2,3-dicyano-p-benzoquinone (98) with cyclopentadiene in MeOH produces the single cycloadduct (99) (Scheme 38). ... 

Ethoxypenta-l, 3-diene underwent the Diels-Alder reaction withp-benzoquinone to give the cis-fused diketone I. Selective catalytic hydrogenation (Ni) of I, followed by reduction with lithium aluminum... 

Diels-Alder reactions with furans constitute a major class of cycloaddition reactions, which have been used for the preparation of a variety of new compounds. Some examples will be given in this section. A one-pot stereoselective synthesis of tricyclic -y-lactones was achieved via Diels-Alder reactions of 2-methoxyfuran with masked o-benzoquinones, which are in turn available from the corresponding 2-methoxyphenols <99CC713>. 

The cycloaddition reactions of 368 (X = CO) with 7V-phenylmaleimide, p-benzoquinone, dimethyl acetylenedicarboxylate, and tetracyanoethylene afforded [4 + 2]-cycloadducts with endo-stereochemistry ethyl acrylate gave two isomers (probably endo and exo). l,4-Dihydro-l,4-oxidonaph-thalene (19) yielded the endo-exo isomer. The Diels-Alder reaction of 368 (X = SO2) with ethyl acrylate gave a mixture of isomers, from which the higher melting product could be isolated in pure form. ... 

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... 

Molecular electrostatic potentials have been used to explain the regioselectivity exhibited in the Diels-Alder cycloaddition reactions between 1-trimethylsilyloxy-butadiene and the quinones 5-formyl-8-methyl-1,4-naphthoquinone, 5-methoxy-7-methyl-1,4-phenanthrenequinone, and 5,6,7-trimethyl-1,4-phenanthrenequinone.128 The intramolecular Diels-Alder reaction of masked o-benzoquinones (123) with a variety of dienes provides adducts (124) which rearrange to functionalized ris-decal ins (125) with complete stereocontrol of up to five stereocentres. This methodology ... 

Recently, the reaction of masked ortho-benzoquinone [92] with C60 was tested [93]. The [4+2] cycloaddition reaction of such electron-deficient dienes with fullerenes resulted in the formation of highly functionalized bicyclo [2.2.2] octenone-fused fullerenes. The reactants were generated in situ by the oxidation of the readily available 2-methoxy phenols with hypervalent iodine agents. For the several different masked ortho-benzoquinones that were tested, it was found that the yield of the cycloadducts depends on the nature of the starting materials and the reaction conditions. Other Diels-Alder reactions of such electron-deficient dienes with electron-poor fullerenes involved tropones [94], 1,3-butadienes substituted with electron-withdrawing groups [95], and 2-pyrone [96]. 

Diels-Alder reactions. The laboratories of Breslow and of Grieco have reported that water can enhance the rate of Diels-Alder reactions of dienes that possess carboxylic acid or similar hydrophilic groups (12, 314). Liotta et al. have examined solvent effects on cycloaddition reactions of benzoquinones with dienes substituted with a relatively hydrophobic group, and report significant rate enhancement in ethylene glycol relative to benzene (26 1) or even to reactions in the absence of a solvent. They attribute the solvent effect to aggregation of the diene and the quinone. 

Carmen Carreno and co-workers have investigated Diels-Alder reactions of a wide variety of benzoquinone-based chiral vinyl sulfoxide dienophiles (Fig. 9). 

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