The DBU-H2O complex as a new catalyst for aldol condensation reactions

Finding new Brønsted-type basic catalysts that can perform condensation reactions of interest to fine chemistry with good activities and selectivities is a constant challenge. In this communication we report the activity of the DBU-H2O system as a basic catalyst for aldol condensation reactions. Diazabicyclo [5.4.0] undec-7-ene (DBU) is a non-nucleophilic, strong tertiary amine base that is widely used in organic synthesis. We demonstrate that DBU, which has Lewis basic properties is inactive for aldol condensation reactions. However when it reacts with equimolar amounts of water it transforms towards a second resonance structure with Brønsted basic properties and therefore, high activity for these reactions. Besides, the DBU-H2O complex is found to be very efficient with reusability for several times.