This result confirms that the dienophile
containing an electron-donating group is not conducive to the DA reaction, and while the [E.sub.a], [E.sub.i], and [n.sub.Mayer] values of BD + MA are the smallest, they seem to be affected by the presence of an electron-withdrawing group, which is relatively favourable for the reaction.
The first step at higher temperature leads to a twofold contribution: the increase of molecular mobility, which allows easier recombination of diene and dienophile
groups, and the triggering of the rD-A reaction, which entail the increase of reactive groups available.
Based on such theoretical calculations the influence of the combination and positional relationship of the substituents of each dienophile
can be analysed in order to develop most suitable reactions for the design of possible precursor to be integrated in synthetic sequences.
Dienes and dienophiles
were adsorbed separately on different samples of activated silica by dissolving them in organic solvents and adding silica while stirring.
With the new approach, says Corey, "the chemzyme brings together the diene and dienophile
in a very specific three-dimensional arrangement that gives only one of the 16 possible products.
The subject invention further reveals a rubbery composition which is comprised of the reaction product of (I) a rubbery polymer having repeat units which are comprised of (1) an olefin monomer selected from the group consisting of conjugated diolefin monomers and monoolefm monomers and (2) a conjugated triene monomer and (II) a dieno phile and/or dienophile
which is functionalized with a group which is capable of reacting with a filler selected from the group consisting of carbon black, silica, starch, and cellulose.
This group is extruded during the reaction as nitrogen gas, but has the important effect of improving the energetics of orbital overlap between the dienophile
(indole olefin) and the diene (Bodwell and Li, Organic Letters 2002:4, 127).
1:45 SYNTHESIS OF A CHIRAL DIENOPHILE
FROM D-GLUCOSE, Joseph R.
The signature of reversion, conjugated unsaturation in the backbone, serves as the reaction site for crosslink repair via the Diels-Alder reaction using the dienophile
1,3 bis(citraconimidomethyl) benzene (BCI-MX, Perkalink 900) (ref.
Increasing the reactivity of the other component (dienophile
3) by introduction of a nitro group did the trick, and the Diels Alder cycloadduct was obtained in 60% yield with 72% diastereoselectivity.