Sharp difference in the rate of formation and stability of the Diels–Alder reaction adducts with 2,3‐dicyano‐1,4‐benzoquinone and N‐phenylimide‐1,4‐benzoquinone‐2,3‐dicarboxylic acid

Abstract

This work reports new studies of the activity and Diels–Alder kinetics of a series of dienophiles: tetracyanoethylene (1), 2,3‐dicyano‐p‐benzoquinone (10), and N‐phenylimide‐1,4‐benzoquinone‐2,3‐dicarboxylic acid (11). Rate differences are interpreted in terms of the donor–acceptor properties of the reagents. The relative π‐acceptor properties of the dienophiles are probed by measuring their interaction energies with a series π‐donor solvents: benzene, toluene, o‐xylene, and chlorobenzene. The normalized interaction energies of 1, 10, and 11 are found to be 100:64:28. Despite the increased energy of the donor–acceptor interaction, dienophile 10 is 255 times less active in the reaction with 9,10‐dimethylanthracene than 11. It is suggested that this is due to the significantly lower energy of π‐bond cleavage in bicyclic dienophile 11, compared with monocyclic 10.

High pressure, temperature, and solvent effect on the Diels–Alder cycloaddition reaction between thiobenzophenone and cyclopentadiene

“…Figure 1 shows that the reactivity of 7 is most sensitive to the changes in the ionization potential of the diene. The larger value of the ln k 2 versus IP slope seen for 7 (line 2 in Figure 1) confirms the fact that it is a strong π‐acceptor 36 . The similar slopes seen for the lines 1, 3, and 4 indicate that 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione, thiofluorenone, and maleic anhydride have moderate and approximately the same π‐acceptor properties.…”

“…The larger value of the lnk 2 versus IP slope seen for 7 (line 2 in Figure 1) confirms the fact that it is a strong π-acceptor. 36 The similar slopes seen for the lines 1, 3, and 4 indicate that 4-phenyl-1,2,4-triazoline-3,5-dione, thiofluorenone, and maleic anhydride have moderate and approximately the same π-acceptor properties. Therefore, the increased activity of thiofluorenone compared with maleic anhydride and the increased activity of 4-phenyl-1,2,4triazoline-3,5-dione compared with tetracyanoethylene in reactions with substituted butadienes cannot be explained by the difference in the energy of orbital interactions.…”