Polymer‐supported bases. 7. Nucleophilic acyl rearrangements catalyzed by polymer‐supported aminopyridine or imidazole bases

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Abstract
Polymer‐supported aminopyridine or imidazole catalysts were effective for acyl rearrangements of O‐acylated substrates to C‐acylated products. Some of the aminopyridine catalysts, which had much higher activity than the imidazole catalyst, exhibited high activity comparable to that of the corresponding soluble catalyst, 4‐N, N‐dimethylaminopyridine. The activity of the immobilized aminopyridines was studied as a function of the percentage of ring substitution, spacer‐chain length, and solvents. The affinity of the substrates for the immobilized catalysts played an important role for the rearrangements. The increased catalytic activity resulted from the increased affinity of the substrates for the catalysts. The activity of the immobilized bases decreased gradually owing to the reaction of the active site with the products as the catalysts were used repeatedly. The treatment of the used catalysts with nucleophiles restored the activity to some extent. The activity decrease can be minimized by shortening a contact time between the catalysts and the products.

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