Diels-Alder reaction butadiene + ethylene

Bernardi F, Bottom A, Field MJ, Guest MF, Hillier IH, Robb MA, Venturini A. MC-SCF study of the Diels-Alder reaction between ethylene and butadiene. J Am Chem Soc 1988 110 3050-3055. 

Berski, S., Andres, J., Silvi, B., Domingo, L. R. (2003). The joint use of catastrophe theory and electron localization function to characterize molecular mechanisms. A density functional study of the Diels-Alder reaction between ethylene and 1,3-butadiene. J. 

In the Diels-Alder reaction, an ethylene derivative dienophile) reacts with a 1,3-diene to form a cyclohexene, the simplest case being the reaction of ethylene with 1,3-butadiene,... 

Another kind of reaction that is formally closely related to the electrocyclic reaction is the cycloaddition reaction, exemplified by the Diels-Alder reaction between ethylene and butadiene to give cyclohexene (I). Such reactions are classified in terms of the... 

Elastomers. Ethylene—propylene terpolymer (diene monomer) elastomers (EPDM) use a variety of third monomers during polymerization (see Elastomers, ethyiene-propylene-diene rubber). Ethyhdenenorbomene (ENB) is the most important of these monomers and requires dicyclopentadiene as a precursor. ENB is synthesized in a two step preparation, ie, a Diels-Alder reaction of CPD (via cracking of DCPD) with butadiene to yield 5-vinylbicyclo[2.2.1]-hept-2-ene [3048-64-4] (7) where the external double bond is then isomerized catalyticaHy toward the ring yielding 5-ethyhdenebicyclo[2.2.1]-hept-2-ene [16219-75-3] (ENB) (8) (60). 

Cycloaddition involves the combination of two molecules in such a way that a new ring is formed. The principles of conservation of orbital symmetry also apply to concerted cycloaddition reactions and to the reverse, concerted fragmentation of one molecule into two or more smaller components (cycloreversion). The most important cycloaddition reaction from the point of view of synthesis is the Diels-Alder reaction. This reaction has been the object of extensive theoretical and mechanistic study, as well as synthetic application. The Diels-Alder reaction is the addition of an alkene to a diene to form a cyclohexene. It is called a [47t + 27c]-cycloaddition reaction because four tc electrons from the diene and the two n electrons from the alkene (which is called the dienophile) are directly involved in the bonding change. For most systems, the reactivity pattern, regioselectivity, and stereoselectivity are consistent with describing the reaction as a concerted process. In particular, the reaction is a stereospecific syn (suprafacial) addition with respect to both the alkene and the diene. This stereospecificity has been demonstrated with many substituted dienes and alkenes and also holds for the simplest possible example of the reaction, that of ethylene with butadiene ... 

Table 12.1 Diels-Alder reaction of butadiene and ethylene to form cyclohexene...

Let us finally consider two Z-matrices for optimization to transition structures, the Diels-Alder reaction of butadiene and ethylene, and the [l,5]-hydrogen shift in Z-1,3-pentadiene. To enforce the symmetries of the TSs (Cj in both cases) it is again advantageous to use dummy atoms. 

The chemical reactions through cyclic transition states are controlled by the symmetry of the frontier orbitals [11]. At the symmetrical (Cs) six-membered ring transition state of Diels-Alder reaction between butadiene and ethylene, the HOMO of butadiene and the LUMO of ethylene (Scheme 18) are antisymmetric with respect to the reflection in the mirror plane (Scheme 24). The symmetry allows the frontier orbitals to have the same signs of the overlap integrals between the p-or-bital components at both reaction sites. The simultaneous interactions at the both sites promotes the frontier orbital interaction more than the interaction at one site of an acyclic transition state. This is also the case with interaction between the HOMO of ethylene and the LUMO of butadiene. The Diels-Alder reactions occur through the cyclic transition states in a concerted and stereospecific manner with retention of configuration of the reactants. 

In contrast with exo (top) facial selectivity in the additions to norbomene 80 [41], Diels-Alder reaction between isodicyclopentadiene 79 takes place from the bottom [40] (see Scheme 32). To solve this problem, Honk and Brown calculated the transition state of the parent Diels-Alder reaction of butadiene with ethylene [47], They pointed ont that of particular note for isodicyclopentadiene selectivity issue is the 14.9° out-of-plane bending of the hydrogens at C2 and C3 of butadiene. The bending is derived from Cl and C4 pyramidalization and rotation inwardly to achieve overlap of p-orbitals on these carbons with the ethylene termini. To keep the tr-bonding between C1-C2 and C3-C4, the p-orbitals at C2 and C3 rotate inwardly on the side of the diene nearest to ethylene. This is necessarily accompanied by C2 and C3 hydrogen movanent toward the attacking dienophile. They proposed that when norbomene is fused at C2 and C3, the tendency of endo bending of the norbomene framework will be manifested in the preference for bottom attack in Diels-Alder reactions (Schane 38). 

Goldstein, E., Beno, B., Houk, K. N., 1996, Density Functional Theory Prediction of the Relative Energies and Isotope Effects for the Concerted and Stepwise Mechanism of the Diels-Alder Reaction of Butadiene and Ethylene , J. Am. Chem. Soc., 118, 6036. 

A combination of a metathesis and a Diels-Alder reaction was published by North and coworkers [263]. However, this is not a true domino reaction, as the dienophile (e. g., maleic anhydride) was added after the in situ formation of the his-butadiene 6/3-89 from the fois-alkyne 6/3-88 and ethylene. The final product is the fois-cycloadduct 6/3-90, which was obtained in 34% yield. Using styrene as an un-symmetrical alkene instead of ethylene, the mono-cycloadduct 6/3-91 was formed as a mixture of double-bond isomers, in 38% yield (Scheme 6/3.26). 

The most simple Diels-Alder reaction, that between butadiene and ethylene, represented schematically in Figure 3, has been extensively studied employing several methods of calculation. The results obtained have initiated some controversy regarding the nature of... 

FIGURE 3. Schematic representation of the transition state of the Diels-Alder reaction between butadiene and ethylene... 

Figure 5.60 The transition-state region of the reaction profile (along the IRC) for the model butadiene + ethylene Diels-Alder reaction. (The zero of energy corresponds to the cyclohexene product.)...

Mechanistic and theoretical studies of the Diels-Alder reaction have resulted in the characterization of this reaction as a concerted, although not necessarily synchronous, single-step process28-31 45. The parent reaction, the addition of 1,3-butadiene to ethylene yielding cyclohexene, has been the subject of an ongoing mechanistic debate. Experimental results supported a concerted mechanism, whereas results from calculations seemed to be dependent on the method used. Semi-empirical calculations predicted a stepwise mechanism, whereas ab initio calculations were in favor of a concerted pathway. At the end of the 80s experimental and theoretical evidence converged on the synchronous mechanism29-31. 

The Diels-Alder reaction is the best known and most widely used pericyclic reaction. Two limiting mechanisms are possible (see Fig. 10.11) and have been vigorously debated. In the first, the addition takes place in concerted fashion with two equivalent new bonds forming in the transition state (bottom center, Fig. 10.11), while for the second reaction path the addition occurs stepwise (top row, Fig. 10.11). The stepwise path involves the formation of a single bond between the diene (butadiene in our example) and the dienophile (ethylene) and (most likely) a diradical intermediate, although zwitterion structures have also been proposed. In the last step, ring closure results with the formation of a second new carbon carbon bond. Either step may be rate determining. 

Fig. 10.11 The stepwise and concerted mechanisms for the Diels-Alder reaction between butadiene and ethylene. The reactants (lower left) proceed to the product, cyclohexene (lower right) either through a two step, two transition state mechanism involving the formation of a diradical intermediate (top center), or more directly through the symmetric synchronous transition state (bottom center) (Storer, J. W., Raimondi, L., and Houk, K. N., J. Am. Chem. Soc. 116, 9675 (1994))...

The behavior described above has been verified by experiment and calculation on numerous substituted dienes and dienophiles. For example Fig. 10.13 shows results for 2°-D isotope effects on Diels-Alder reactions of 2-methyl-butadiene with cyano-ethylene and 1,1-dicyano-ethylene. The calculated and experimental isotope effects are in quantitative agreement with each other and with the results on (butadiene + ethylene). In each case the excellent agreement between calculated and observed isotope effects validates the concerted mechanism and establishes the structure of the transition state as that shown at the bottom center of Fig. 10.11 and the left side of Fig. 10.12a. 

The prototype hole-catalyzed Diels-Alder reaction between the butadiene radical cation and ethylene has also been studied by Bauld [53]. He finds strongly exothermic formation of a l-hexene-3,6-diyl radical cation intermediate without activation energy followed by a weakly activated (activation energy 2.3 kcal mol ) closure of the second C-C bond to form the cyclohexene radical cation, The reaction shows no overall activation energy relative to the... 

In the Diels-Alder reaction, a diene, such as 1,3-butadiene, reacts with a dienophile, such as ethylene, to form a product with a six-membered ring. This is an important reaction, not only to students trying to pass Organic Chemistry, but also in organic synthesis. 

The real reactions that most resemble these are the production of cyclobutane from two ethylene molecules ((112)2) and the Diels-Alder reaction between butadiene and ethylene ((H2)3). Even these cannot be made to react in the bare forms, but fairly simple activation by substituents will allow the (H2)3 analog to proceed. Apparently, no form of the (1 2)2 analog has ever been observed. Our analysis suggests that there is a fundamental difference between the four-electron and six-electron systems that produces the effect. The book by Woodward and Hoffrnan[58] may be consulted for a rationalization of these results based upon MO theory. 

In the area of reaction energetics. Baker, Muir, and Andzehn have compared six levels of theory for the enthalpies of forward activation and reaction for 12 organic reactions the unimolecular rearrangements vinyl alcohol -> acetaldehyde, cyclobutene -> s-trans butadiene, s-cis butadiene s-trans butadiene, and cyclopropyl radical allyl radical the unimolecular decompositions tetrazine -> 2HCN -F N2 and trifluoromethanol -> carbonyl difluoride -F HF the bimolecular condensation reactions butadiene -F ethylene -> cyclohexene (the Diels-Alder reaction), methyl radical -F ethylene -> propyl radical, and methyl radical -F formaldehyde -> ethoxyl radical and the bimolecular exchange reactions FO -F H2 FOH -F H, HO -F H2 H2O -F H, and H -F acetylene H2 -F HC2. Their results are summarized in Table 8.3 (Reaction Set 1). One feature noted by these authors is... 

The Diels-Alder reaction is one of the most important carbon-carbon bond forming reactions,521 522 which is particularly useful in the synthesis of natural products. Examples of practical significance of the cycloaddition of hydrocarbons, however, are also known. Discovered in 1928 by Diels and Alder,523 it is a reaction between a conjugated diene and a dienophile (alkene, alkyne) to form a six-membered carbo-cyclic ring. The Diels-Alder reaction is a reversible, thermally allowed pericyclic transformation or, according to the Woodward-Hoffmann nomenclature,524 a [4 + 2]-cycloaddition. The prototype reaction is the transformation between 1,3-butadiene and ethylene to give cyclohexene ... 

As a consequence of the concerted mechanism, the Diels-Alder reaction is also stereoselective, implying that the relative configuration of the groups of the reactants is retained. Besides the numerous examples of heterosubstituted compounds,521,522 this was also proved by 1,3-butadiene and ethylene labeled with deuterium [Eqs. (6.88) and (6.89)] 531... 

Although ion-molecule processes would be possible in some electron impact reactions, this process would not lead to the formation of dimeric products formed in the present experiments (20). Ethylene was the major gaseous product. Ethylene and butadiene may be produced from the reverse Diels-Alder reaction of cyclohexene (10) since they were also... 

Figure 7.15 An orbital correlation diagram for the Diels-Alder reaction. The if/A and y/n orbitals at the left are for ethylene, while the others at the left are for butadiene. The orbitals on the right are for the product.

When 3,4-dihydro-2//-pyran (555) is given pulses of a laser beam, it decomposes by a retro-Diels-Alder reaction into acrolein and ethylene (78JA6111). 4-Methyl-5,6-dihydro-2//-pyran (555a) when irradiated in methanol through which oxygen is passed gives a mixture of four cyclic products on treatment with sodium borohydride (79JCS(P1)1806). Pyrolysis of the dihydropyran (555) at 350 °C yields butadiene. 

The simplest of all Diels-Alder reactions, cycloaddition of ethylene to 1,3-butadiene, does not proceed readily. It has a high activation energy and a low reaction rate. Substituents such as C=0 or C=N, however, when directly attached to the double bond of the dienophile, increase its reactivity, and compounds of this type give high yields of Diels-Alder adducts at modest temperatures. 

Diels-Alder reaction, 169-170 aromatic TS, 151 benzyne, 160 butadiene + ethylene, 169 diastereoselectivity, 292 interaction diagram, 169 orbital analysis, 169-170 orbital correlation diagram, 198, 201 reverse demand, 169 substituent effects, 169-170 Diethyl tartrate, 11 Difluorocarbene ( CF2), 115... 

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