Reverse Diels-Alder

Literature articles, which report the formation and evaluation of difunctional cyanoacrylate monomers, have been published. The preparation of the difunctional monomers required an alternative synthetic method than the standard Knoevenagel reaction for the monofunctional monomers, because the crosslinked polymer thermally decomposes before it can revert back to the free monomer. The earliest report for the preparation of a difunctional cyanoacrylate monomer involved a reverse Diels-Alder reaction of a dicyanoacrylate precursor [16,17]. Later reports described a transesterification with a dicyanoacrylic acid [18] or their formation from the oxidation of a diphenylselenide precursor, seen in Eq. 3 for the dicyanoacrylate ester of butanediol, 7 [6]. 

Within the diastereomeric switch sequences, the corresponding trans-diols become accessible either using a Mitsunobu inversion or a reversible Diels-Alder cyclization as key reaction step [249,250]. This synthetic strategy is complementary to an approach involving metabolic engineering of E. coli via the chorismate/ isochorismate pathway [251]. 

The Diels-Alder reaction is usually reversible and has been used to protect double bonds. A convenient substitute for butadiene in the Diels-Alder reaction is the compound 3-sulfolene since the latter is a solid that is easy to handle while the former is gas. " Butadiene is generated in situ by a reverse Diels-Alder reaction (see 17-20). 

On heating, bicyclo[2.2.1]hept-2,3-en-7-ones (48) usually lose CO to give cyclohexadienes, in a type of reverse Diels-Alder reaction. Bicyclo[2.2.1]hepta-dienones (49) undergo the reaction so readily (because of the stability of the benzene... 

Scheme 18 Separation of zingiberene from ginger oil using a selective and reversible Diels-Alder reaction with phenyl l,2,4-triazoline-3,5-dione (PTAD) [105]...

Figure 1.14 Reversible Diels-Alder reaction of substituted fulvenes with diethy Icyanofumarate.

Figure 1.15 Recognition-mediated selectivity in a reversible Diels-Alder DCL.

Boul, P. J. Reutenauer, R Lehn, J.-M. Reversible Diels-Alder reactions for the generation of dynamic combinatorial libraries. Org. Lett. 2005, 7, 15-18. 

A Furan enters into a cycloaddition reaction with the dienophile diethyl acetylcnedicarboxylate to form an adduct. Catalytic reduction occurs preferentially at the more electron-rich double bond of the adduct, and the dihydro product, upon heating, undergoes a reverse Diels-Alder reaction to release ethene and the diesier (Scheme 6.29),... 

Cyclic conjugated dienes that are s-cis conformation, e.g. cyclopentadiene and 1,3-cyclohexadiene, are highly reactive in Diels-Alder reactions. In fact, cyclopentadiene is reactive both as a diene and as a dienophile, and forms dicyclopentadiene at room temperature. When dicyclopentadiene is heated to 170 °C, a reverse Diels-Alder reaction takes place and reforms the cyclopentadiene. 

For reviews of the reverse Diels-Alder reaction, see Iehihara Synthesis 1987, 207-222 Lasne Ripoll Synthesis 1985, 121-143 Ripoll Rouessac Rouessac Tetrahedron 1978, 34, 19-40 Brown Pyrolytic Methods in Organic Chemistry-, Academic Press. New York, 1980, pp. 259-281 Kwart King Chem. Rev. 1968, 68, 415-447. 

Cycloretersion.6 The reverse Diels-Alder reaction of 1 proceeds at 60° with a half-life of 236 minutes. Cycloreversion of the parent diesler is even slower. 

This reaction is a reverse Diels-Alder Reaction. The orbital considerations controlling the backward reaction are the same as the forward reaction. 

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... 

An important variation of the theme is found in furans with a 3-substituent adjacent to the 2-substituent, for then elimination can give heteroquinone methides , possibly by cyclic mechanisms (71CCC4082). A common type is found in the breakdown of furodysin as illustrated in Scheme 8b (78TL4951), and which is probably reversed Diels-Alder in mechanism it often fails if the carbocyclic ring is seven-membered (75TL1421). 

As a result of their accessibility, dihydropyrans provide a useful source of 4//-pyrans. Indeed one of the earliest syntheses of the parent compound involved the pyrolysis of 2-acetoxy-3,4-dihydropyran (165) (62JA2452). The concomitant formation of acrolein, vinyl acetate and acetic acid indicates that a reverse Diels-Alder reaction competes with the pyrolysis. 

Exercise 13-7 The following hydrocarbon degrades on heating by a reverse Diels— Alder reaction. What product(s) does it give ... 

Such a reverse Diels-Alder reaction of benzothiophyne could generate thiophyne ... 

Fig. 25. Nadimide Diels-Alder and reverse Diels-Alder reactions...

Although this work was carried out with a model compound, the results are quite consistent with the mechanisms suggested by the BP team [86] which was working within a bisnadimide. However, the work of Meador et al. [42] presents some diverging conclusions by minimizing the role of the reverse Diels-Alder reaction in the crosslinking mechanism. 

It is well established [87] that pressure accelerates the Diels-Alder reaction and of course the reverse effect is expected for the reverse Diels-Alder reaction. For example, to obtain a homogeneous disk of neat resin or a composite without void the experimental procedure [88] shown on the Fig. 30 has to be used. 

Scola DA (1985) Some chemical characteristics of the reverse Diels-Alder polyimide, PMR-15. In Gupta MR, Weber WD (eds) Polyimides synthesis, characterization and application (Proceedings of the Second International Conference on Polyimides). Society of Plastics Engineers, Inc, Hopewell Jet, p 247... 

Cyclopentadiene cannot be purchased because it is too reactive and dimerizes to dicyclopentadiene upon storage. If it is needed, it is prepared by heating dicyclopentadiene. Cyclopentadiene is produced in a reverse Diels-Alder reaction. It is distilled from the hoi reaction mixture as it is formed and used immediately. 

The ability of furan to undergo both the forward and reverse Diels-Alder reaction has been used to synthesize 1,3-dioxoles, and the reaction appears to have wide applicability. In Scheme 42 the synthesis of 2-phenyl-l,3-dioxole is shown. The key to the process is the dialcohol (119), which is obtained from vinylene carbonate as shown. The dialcohol (119) has the potential of serving as an intermediate for a variety of 2-substituted 1,3-dioxolanes (73JA7161). 

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