Diels-Alder reaction dienophile, definition

Alkynes substituted with one or two trifluoromethyl groups are also highly reactive dienophiles [9] Indeed, hexafluoro-2-butyne is used increasingly as a definitive acetylenic dienophile in "difficult Diels-Alder reactions. It was used, for example, to prepare novel inside-outside bicycloalkanes via its reaction with cir,trnns -l,3-undecadiene [74] (equation 67) and to do a tandem Diels-Alder reaction with a l,l-bis(pyrrole)methane [75] (equation 68) Indeed, its reactions with pyrrole derivatives and furan have been used in the syntheses of 3,4-bis(tri-fluoromethyl)pyrrole [76, 77] (equation 69) and ],4-bis(trifluoromethyl)benzene-2,3-oxide [78] (equation 70), respectively. 

Olefins can add to double bonds in a reaction different from those discussed in 5-15, which, however, is still formally the addition of RH to a double bond. This reaction is called the ene synthesis44,1 and bears a certain similarity to the Diels-Alder reaction (5-47). For the reaction to proceed without a catalyst, one of the components must be a reactive dienophile (see 5-47 for a definition of this word) such as maleic anhydride, but the other (which supplies the hydrogen) may be a simple alkene such as propene. There has been much discussion of the mechanism of this reaction, and both concerted pericyclic (as shown above) and stepwise mechanisms have been suggested. The reaction between maleic anhydride and optically active PhCHMeCH=CH2 gave an optically active product,441 which is strong evi-... 

Because the reversibility of the Diels—Alder reaction at accessible temperatures was key to the concept of re-mending a polymeric solid, we considered other diene dienophile combinations but were dissatisfied with aU we found in the literature for various reasons, but in the process realized that cyclopentadiene is a molecule that is a diene and a dienophile, a property that was a definite advantage over systems 2 and 3 + 4. This led to our first encounter with Hermann Staudinger. 

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