1,3-Cyclopentadiene, Diels-Alder molecular orbitals

Diels-Alder activation volume, 138, 139, 145 Diels-Alder adduct uses, 145, 146 Diels-Alder with anthracene, 98 Diels-Alder with cyclopentadiene, 87 Diels-Alder with cyclopropane compounds, 132 Diels-Alder entropy of activation, 138 Diels-Alder molecular orbital picture, 140-143 Diels-Alder with nonconjugated dienes, 132 Diels-Alder with poly(furfuryl methacrylate), 472 Diels-Alder reaction dienophile, 103, 120, 138, 140, 142... 

Inagaki, Fujimoto and Fukui demonstrated that ir-facial selectivity in the Diels-Alder reaction of 5-acetoxy- and 5-chloro-l,3-cyclopentadienes, 1 and 2, can be explained in terms of deformation of a frontier molecular orbital FMO [2], The orbital mixing rule was proposed to predict the nonequivalent orbital deformation due to asymmetric perturbation of the substituent orbital (Chapter Orbital Mixing Rules by Inagaki in this volume). 

There has been an ab initio molecular orbital (MO) investigation of the Diels-Alder reaction of iminoboranes with cyclopentadiene which yields 2-aza-3-borabicyclo[2.2.1]hept-5-enes 36 as shown in Equation (1) <2003OM2298>. 

On the basis of Monte Carlo simulations [40] and molecular orbital calculations [26a], hydrogen bonding was proposed as the key factor controlling the variation of the acceleration for Diels-Alder reactions in water. Experimental differences of rate acceleration in water-promoted cycloadditions were recently observed [41]. Cycloadditions of cyclopentadiene with acridizinium bromide, acrylonitrile and methyl vinyl ketone were investigated in water and in ethanol for comparison (Scheme 3). Only a modest rate acceleration of 5.3 was found with acridizinium bromide, which was attributed to the absence of hydrogenbonding groups in the reactants. The acceleration factor reaches about 14 with acrylonitrile and 60 with methyl vinyl ketone, which is the best hydrogen-bond acceptor [41]. 

Q 1. Cyclopentadiene reacts with acrylic ester to give products of Diels—Alder reaction. What are the interacting frontier molecular orbitals ... 

Computational studies of the Diels—Alder reaction of cyclopentadiene with ketene at the C=0 and C=C bonds were used for comparison to the corresponding reactions of allene and ketenimine. The reactivities were dependent on the distortion energy arising from the folding energy and molecular strain, and the interaction energy from orbital interaction, closed-sheU repulsion, and static repulsion (Eqn (4.105)). ... 

Figure 13.13 Diels-Alder reaction of cyclopentadiene and maleic anhydride, (a) When the highest occupied molecular orbital (HOMO) of the diene (cyclopentadiene) interacts with the lowest unoccupied molecular orbital (LUMO) of the dienophile (maleic anhydride), favorable secondary orbital interactions occur involving orbitals of the dienophile. (b) This interaction is indicated by the purple plane. Favorable overlap of secondary orbitals (indicated by the green plane) leads to a preference for the endo transition state shown.

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