Double Diels-Alder addition

The sunuhaneous double Diels-Alder addition of l,l-bis(3,5-dimethylfur-2-yl)ethane (8) with a biS dienophile such as diethyl ( , )-4-oxohepta-2,5-diene-1,7-dioate was proposed as new, asymmetric synthesis of long-chain polypropionate fragments and analogues <96TL4149>. 

Scheme 10.26 Regioselective tethered double Diels-Alder-additions to Q,...

Scheme 1.6. Regio- and diastereoselective double Diels-Alder addition to Cgo using a threitol derivative as imprinting template.

Formation of Bis-adducts by Double Diels-Alder Addition of Tethered Bis(buta-l,3-diene)s to C o... 

Nishimura and co-workers used bis(o-quinodimethanes) connected by a.n+dioxa-methylene tethers for the regioselective bis-functionalization by double Diels-Alder addition (Scheme 7-14) [93]. The tethered bis(o-quinodimethanes) were intermediately formed by heating the bis(bromomethyl) derivatives 72a-d together with C, in toluene in the presence of KI and [18]crown-6 [90]. With an 0-(CH2)2-0 tether (72a), the cis-2 and cw-3 bis-adducts 73a and ( )-74a were isolated in 10% and 8% yield, respec-... 

Scheme 7-14 Regioselective bis-functionalizations by double Diels-Alder addition of tethered bis(o-quinodimethanes) to Cgo [93, 94].

Development of synthetic routes to the anthracycline antibiotics is important because of the cytotoxic properties of many of these compounds. A short route " to possible intermediates proceeds via double Diels-Alder addition to (16). The problem of the availability of (16) has been overcome " by efficient palladium-catalysed carbomethoxylation of the furan-maleic anhydride Diels-Alder adduct to give (122) in 92% yield. Elaboration of Diels-Alder adducts of (16) to anthracyclines requires rupture of the ether bridge. Acid-catalysed ringopening " in simple 7-oxabicyclo[2.2.1]heptanes has been studied. 

Intramolecular cycloaddition of azomethine imines and olefins has been used to synthesize various diazabicyclic systems (Scheme 29). A double Diels-Alder addition of coumalic acid with butadienes has been used to prepare tricyclo[3,2,l,0 ]oct-3-enes (475). ... 

The monomer, norbomene (or bicyclo[2.2.l]hept-2-ene), is produced by the Diels-Alder addition of ethylene to cyclopentadiene. The monomer is polymerised by a ring-opening mechanism to give a linear polymer with a repeat unit containing both an in-chain five-membered ring and a double bond. Both cis-and trans- structures are obtainable according to the choice of catalyst used ... 

A somewhat more complex application of this notion is represented by the CNS stimulant fencamfine (83). Diels-Alder addition of cyclopentadiene and nitrostyrene affords the norbomene derivative, 80. Catalytic hydrogenation reduces both the remaining double bond and the nitro group (81). ° Condensation with acetaldehyde gives the corresponding imine (82) a second reduction step completes the synthesis of fencamfine (83). ... 

Complexes 17-19 can be written in one valence structure as a, /3-unsaturated carbonyl compounds in which the carbonyl oxygen atom is coordinated to a BF2(OR) Lewis acid. The C=C double bonds of such organic systems are activated toward certain reactions, like Diels-Alder additions, and complexes 17-19 show similar chemistry. Complexes 17 and 18 undergo Diels-Alder additions with isoprene, 2,3-dimethyl-1,3-butadiene, tram-2-methyl-l,3-pentadiene, and cyclopentadiene to give Diels-Alder products 20-23 as shown in Scheme 1 for complex 17 (32). Compounds 20-23 are prepared in crude product yields of 75-98% and are isolated as analytically pure solids in yields of 16-66%. The X-ray structure of the isoprene product 20 has been determined and the ORTEP diagram (shown in Fig. 3) reveals the regiochemistry of the Diels-Alder addition. The C-14=C-15 double bond distance is 1.327(4) A, and the... 

Diels-Alder additions to 17-19 parallel the known Diels-Alder additions to vinyl substituted Fischer carbene complexes (34). It appears that both M(CO)5 carbene moieties, where M is Cr or W, and (ferra-/3-diketonato)BF2 substituents can activate C=C double bonds toward Diels-Alder additions. 

As can be seen from the double-cisoid conformation in Scheme 5.50, a Diels-Alder addition (with the generalized dienophile 283) could in principle yield either the mono-adduct 334 or the alternative 335. At least for the reaction with 1,2,4,6-octatetraene (211), it was shown that the former addition mode is preferred, the driv-... 

The new absorption band at 435 ran in the C60 spectrum has been attributed to the 1,2 addition to the fullerene cage to the fatty acid chains either across to the double bonds by a Diels-Alder addition or, more simply, by radical addition (Cataldo and Braun, 2007). Thus, fatty acid esters are able to not only dissolve C60, but also react with this molecule causing the addition of the fatty chain to the fullerene cage. In fact, the bands at 435 ran shown in Fig. 13.3 appear only when C60 is stirred at 75°C for a couple of hours in the esters of fatty acids. Only for olive oil the new band appears much weaker than in the other cases and displaced at 450 ran (Fig. 13.3B). Since this oil contains chlorophyll, the displacement may be probably due also to a charge-transfer interaction between C60 and chlorophyll or with other impurities. 

The first example illustrates how a 1,4-dehydroaromatic system with cyclohexane ring having two double bonds may be also disconnected according to a retro-Diels-Alder to give a diene and an acetylene as the dienophile [25]. The second example makes clear that even an aromatic double bond may be -in some instances-involved in a retrosynthetic pericyclic disconnection [26]. In the synthetic direction, the polycyclisation involves a conrotatory electrocyclic cyclobutene ring opening, (16 15) followed by an intramolecular Diels-Alder addition (see Scheme... 

Regiochemistry of Multiple Additions 10.3.3.4 Double Diels-Alder Tethers... 

Indole reacts with dimethylacetylene dicarboxylate giving tetramethylcar-bazol-l,2,3,4-tetracarboxylate as a major product,formed via 384 (R = H, and/or geometric isomer) and then Diels-Alder addition and dehydrogenation. /V-Acetylindole undergoes an extraordinary double condensation and cyclization with methyl acrylate in the presence of palladium(II) acetate in acetic acid giving 9% of the dimethyl 9-acetylcarbazole-2,3-dicar-boxylate 393 as well as 394 and 395, the products of monosubstitution at the indole a and S-positions. ... 

In practice, the adduct with the endo2 configuration usually is the major product. As a general rule, Diels-Alder additions tend to proceed to favor that orientation that corresponds to having the diene double bonds and the unsaturated substituents of the dienophile closest to one another. This means that addition by Equation 13-3 is more favorable than by Equation 13-4, but the degree of endo-exo stereospecificity is not as high as the degree of stereospecificity of suprafacial addition to the diene and dienophile. 

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