Unusually Lowered Acidity of Ammonium Group Surrounded by Crown Ether in a Rotaxane System and Its Acylative Neutralization

Acidity of a secondary ammonium group in a rotaxane system with a crown ether was unusually lowered. N-Acylation of the ammonium group by acid anhydrides or chlorides proceeded slowly in the presence of excess tertiary amine to give the N-acylated rotaxanes without salt structure.