Ultrasound-mediated synthesis of camphoric acid-based chiral salens for the enantioselective trimethylsilylcyanation of aldehydes.

New chiral salen ligands were prepared by the ultrasound-irradiated condensation of optically active (1R, 3S)-1,2,2-trimethyl-1,3-diaminocyclopentane with aromatic 1-hydroxyaldehydes. The ultrasound-mediated process is more convenient due to shorter reaction times, energy economy, and easier isolation of the products. The in situ formed Ti(IV)(salen) complexes, evaluated as catalysts in the enantioselective trimethylsilylcyanation of benzaldehyde, were found to be efficient for this process, originating the corresponding product in high yields (72-99%) and selectivities of up to 79%. The lowest energy transition states were determined by computational studies. These results were in qualitative agreement with the experimentally observed ones. 2009 Wiley-Liss, Inc.