Polymer-Supported Bases. XI. Esterification and Alkylation in the Presence of Polymer-Supported Bicyclic Amidine or Guanidine Moieties

Polymer-supported 1,5,7-triazabicyclo[4.4.0]deca-5-ene (TBD) was prepared by the reaction of chloromethylated polystyrene resins, cross-linked with 2 mol% of divinylbenzene, with TBD. The reaction of benzoic acid with bromobutane was carried out in toluene or acetonitrile in the presence of polymer-supported TBD or polymer-supported 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The rate of esterification was dependent on the ring substitution of the supported bases and the solvent. The reduced ring substitution resulted in the increased swellability of the polymeric beads containing benzoate or bromide ions for toluene and thereby in the increased reaction rate. The rate with the high ring-substituted bases increased in acetonitrile, because of the high swellability of the immobilized salts and the high nucleophilicity of benzoate anion in the solvent. The supported bases were also effective for alkylation of an active methylene compound with bromoalkane.