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.