Diels-Alder cyclopentadiene+ethene

Compare electrostatic potential maps for the following Diels-Alder transition states cyclopentadiene+ethene, cyclopentadiene+acrylonitrile and cyclopentadiene+ tetracyanoethylene, with those of reactants cyclopentadiene, ethene, acrylonitrile and tetracyanoethylene. Are electrons transferred from diene to dienophile in the transition states (relative to reactants) or vice versa For which reaction is the transfer the greatest The least Quantify your conclusion by measuring the total charge on the diene and dienophile components in the three transition states. 

Density functional theory has been used to investigate the Diels-Alder reactions of triazolinedione with s-cis- and. y-fran -butadiene. " Combined quantum mechanics-molecular mechanics calculations have been used to investigate the asymmetric Diels-Alder reaction of cyclopentadiene with the complex dienophiles AICI3-methyl acrylate and methoxyaluminium dichloride-acrolein.Equilibrium constants have been determined for the molecular complexes formed from 1-alkyl-1-(2-naphthyl)ethenes and 1-vinylnaphthalene with TCNE in C1(CH2)2C1 at 27.1 °C ... 

Monomers are shown in Table 2.1 and in Figure 2.1. The most important monomer is norbornene. Norbornene is in made from di-cyclopentadiene (DCPD) and ethene by a Diels-Alder reaction. 5-Tri-ethoxysilyl-2-norbomene is used for crosslinkable compositions (2). 

The left division corresponds to a simple [4 + 2] cycloaddition, whereas the right division corresponds to a complex reaction involving formation of three ring bonds at once. Actual Diels-Alder reactions require diene and dienophile starting materials, and two possibilities, using 1,3-cyclopentadiene as the diene and ethene or ethyne as dienophile, follow ... 

Cyclopentadiene is such a reactive 1,3-diene that it undergoes Diels-Alder reactions with all cyano-substituted ethenes. The rate constants of these cycloadditions (Table 15.1) show that each cyano substituent increases the reaction rate significantly and that geminal cyano groups accelerate more than vicinal cyano groups. 

Diels-Alder reactions of cyclopentadiene with different alkenes proceed at different rates. Cyclopentadiene reacts with acrolein in ether at room temperature (24 h) to give a 95% yield of 27.59 contrasts with the reaction of cyclopentadiene and ethene in ether to give a 74% yield of norbornene (28), but required heating to 200°C in an autoclave at 5800 psi pressure or 32 h. The presence of an electron releasing group on the alkene causes the reaction to proceed with greater difficulty. Vinyl acetate reacted with cyclopentadiene at 190°C in an autoclave (10 h, neat) to give only 25% of 29. 

Cyclopentadiene undergoes a Diels-Alder reaction with ethene at 160-180 °C. Write the structure of the product of this reaction. 

Figure 4.52. A cartoon showing the consequences of the Diels-Alder reaction between cyclopentadiene and ethene to generate bicyclo[2.2.1]heptene (norbornene) and the subsequent catalytic reduction of the latter to produce bicyclo[2.2.1] heptane (norbomane).

Syntheses of norbornenes and norbomadienes having Si-containing substituents as a rule were carried out by the above-mentioned Diels-Alder condensation of cyclopentadiene (or dicyclopentadiene) and Si-containing ethenes or ethynes [177]... 

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