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

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.