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.
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).
The thermally reversible polymer typically includes at least one furan diene unit and at least one amine maleimide dienophile
1:45 SYNTHESIS OF A CHIRAL DIENOPHILE
FROM D-GLUCOSE, Joseph R.
Also discussed are the reactions of cascade cyclizations, heterocyclization involving enyne-carbodiimides, and new achievements in some classical cycloaddition reactions, such as the Diels-Alder condensation with acetylenic dienophiles
, [2+2] cycloadditions with an acetylene component leading to the creation of a cyclobutene ring, and new results in cyclobutene syntheses by [2+2] acyclization of phosphorus containing 1,3-butadiene derivatives synthesized starting with propargyl-type alcohols.
The 1,2,4-triazines can react with electron-rich dienophiles
in an inverse electron demand Diels-Alder reaction.