Diels-Alder reaction maleic compounds

The Diels-Alder Reaction consists in the direct combination of a compound containing a conjugated diene system u ith a reagent which possesses a double or triple bond activated bj suitable adjacent groups. Examples of such reagents are maleic anhydride, p-benzoquinone, acraldehyde and acetylene dicarboxylic esters. Combination always occurs at the 1,4 positions of the diene system ... 

Removal of maleic and fumaric acids from the cmde malononitrile by fractional distillation is impractical because the boiling points differ only slightly. The impurities are therefore converted into high boiling compounds in a conventional reactor by means of a Diels-Alder reaction with a 1,3-diene. The volatile and nonvolatile by-products are finally removed by two vacuum distillations. The by-products are burned. The yield of malononitrile amounts to 66% based on cyanogen chloride or acetonitrile. 

Dicyclopentadienedicarboxyhc acid can undergo a Diels-Alder reaction in the presence of a stoichiometric amount of a dienophile at 140—190°C to give an adduct of the monomeric acid. The yield of adduct is usually 75—95%. A large number of polyfunctional compounds are easily prepared in this manner. The reaction with maleic anhydride gives a tribasic acid. 

Soon after the discovery of the addition reaction between diene-ophiles and dienes which now bears their names, Diels and Alder extended their investigations to include potential heterocyclic dienes. In 1929 the first compound investigated, furan, was observed to combine with maleic anhydride, like butadiene in a typical Diels-Alder reaction, across the 2,5-positions yielding a 1 1 molar adduct... 

Compound 5 can be trapped through a Diels-Alder reaction with maleic anhydride and thus be shown to be an intermediate. Further evidence for a mechanism involving two subsequent allyl conversions has been provided by experiments with " C-labeled substrates. 

On transforming the cyclopentenone 1431 into the trimethylsilyloxy diene 1432 the ensuing Diels-Alder cyclization gives rise to 69% tricychc compound 1433 [10] (Scheme 9.8). For Diels-Alder-reactions of thioaldehydes, selenoaldehydes, or unsaturated nitroso compounds with cyclopentadiene, see the reactions of 602 to 603 and of 605 to 606 in Scheme 5.48 and of 1092 to 1093 in Scheme 7.43. For Diels-Alder-reactions of silyloxyazadienes such as 510 with maleic anhydride to give 511, see Scheme 5.29. 

In general, there is said to be a parallel between the ease of photochemical oxygen addition and that of Diels Alder reaction, and oxygen and maleic anhydride form bridges at the same points in these polynuclear compounds.10... 

Compound 83 is a diene that comprises four carbon atoms of a hexose chain, and it takes part in the Diels-Alder reaction with maleic anhydride to give 86% of the product 84, the stereochemistry of the addition being directed by the acetal ring [42]. 

In the fused compounds (241) and (242) the furan ring fails to react as a diene and Diels-Alder reaction with dienophiles occurs on the terminal carbocyclic rings. However, (243) and (244) afford monoadducts with dimethyl fumarate by addition to the furan rings (70JA972). The rates of reaction (Table 2) of a number of dehydroannuleno[c]furans with maleic anhydride, which yield fully conjugated dehydroannulenes of the exo type (247), have been correlated with the aromaticity or antiaromaticity of the products (76JA6052). It was assumed that the transition state for the reactions resembled products to some extent, and the relative rates therefore are a measure of the resonance energy of the products. The reaction of the open-chain compound (250), which yields the adduct (251), was taken as a model. Hence the dehydro[4 + 2]annulenes from (246) and (249) are stabilized compared to (251), and the dehydro[4 ]annulenes from (245) and (248) are destabilized (Scheme 84). 

Diels-Alder Reaction. By means of the Diels-Alder reaction a considerable number of hydrobiphenyls have been prepared,486 from which it should be possible to obtain unsymmetrical biaryls by dehydrogenation. Only a few of the adducts have been converted to the completely aromatic compounds. o-Terphenyl has been prepared from the adduct of maleic anhydride and 3,4-diphenylcyclopentadienone,436 and p-terphenyl has been obtained in practically quantitative yield from the adduct of the methyl ester of acetylenedicarboxylic acid and 1,4-diphenylbutadiene.43d... 

Maleic anhydride reacts with cyclopenta-1,3-diene in a Diels-Alder reaction. Since there is a plane of symmetry, the reaction can lead to two achiral compounds, which are diastereomers of each other, containing an endo- or exo-oriented dicarboxylic anhydride group. These differ in absolute and relative configuration at the bond shared by both rings. Under normal conditions the Diels-Alder reaction proceeds stereospecifically to yield preferentially the endo product. Note that in the tricyclic product no trans fusion in the ring system is possible as a consequence of the reaction mechanism. Subsequent reduction of the products therefore affords two diols, which are also diastereomers of each other. These may be separated by chromatography on an achiral stationary phase. 

Azo compounds like esters or imides of azo dicarboxylic acid act as reactive dienophiles in normal electron demand hetero Diels-Alder reactions due to the strong activation caused by two electron-withdrawing moieties. In the last years, considerable attention has focused on alkyl and phenyl derivatives of 1,2,4-tria-zoline-3,5-diones since their cycloadditions to chiral dienes proceed with often excellent facial selectivities. Thus, when reacting an oxapropellane derived diene with N -methyltriazolinedione, Paquette et al. obtained the cycloadduct as single diastereomer, but both maleic anhydride and N-phenyl maleimide were distinctly less reactive and turned out to undergo cycloadditions with poor selectivities [289]. 

The aromaticity of a heterocycle depends on how effectively the lone-pair of the heteroatom contributes to the aromatic sextet. The aromaticity of five-membered heterocyclic compounds may be estimated from their reactivity in the Diels-Alder reaction.94 Spectrophotometry shows that furan, thiophene, and selenophene resemble benzene in that with maleic anhydride 1 1 complexes are formed which are stable up to 150°C in the case of thiophene, decompose at 150°C with selenophene (whereby selenium is formed together with a diene which gives a further adduct with another molecule of maleic anhydride), and produce the usual adduct at 20°C with furan. Thus, only furan is a normal diene as regards the Diels-Alder reaction. 

Tetrasubstituted-l,2,3,4,5,6,7,8-octahydrocarbazoles 1137 were synthesized in 46-90% yields by a novel tandem Diels-Alder reaction in one step from A -benzyl-2,5-dimethyl-3,4-bisacetoxymethylpyrrole 1136 and dienophiles such as maleic anhydride, maleimide, ethyl maleate, fumaronitrile, and ethyl acrylate (Scheme 222) <20000L73>. The 2,3,6,7-tetrasubstituted carbazoles 1138 were then synthesized in 29-87% yields from compound 1137 by oxidation with DDQ. 

The total synthesis of complicated polycyclic closed-shell cage compounds represents one of the top achievements of modern synthesis. Progress in this area is mainly due to the ingenious use of the Diels-Alder cycloaddition, as is illustrated in the synthesis of basketene 357 (Scheme 2.123). " In this case the Diels-Alder reaction between diene 358 (the valent isomer form of cyclooctate-traene) and maleic anhydride leads in one step to the construction of the tricyclic structure 359 in quantitative yield. Subsequent [2 -I- 2] cycloaddition (see below) leads to product 360, which has the required structure but additional substituents. Saponification and oxidative decarboxylation of 360 gives basketene 357. 

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