Preferred Binding of Carboxylates by Chiral Urea Derivatives Containing -Phenylethyl Group

An efficient, simple protocol for the synthesis of a new family of chiral ureas 1 - 4 is described. The binding properties of 1 - 4 toward different anion (acetate, benzoate, fluoride, and chloride) have been studied by H-1-NMR titration and have been observed in the case of 4 is a selective receptor for acetate. The theoretical calculation M06/6-311+G(d,p) helped us explain the binding properties observed. The most interesting observation is that this calculated structure is consistent with expected, based on the concept of allylic 1,3-strain (A(1,3) strain). When chiral caboxylates were studied, urea 1 was the best in discriminating between enantiomers.