The synthesis of a new nitrogen joined N-PEG-TsDPEN ligand and its application in asymmetric transfer hydrogenation of ketones in neat water

A new polyethylene glycol (PEG) supported ligand, with the PEG chain attached to the nitrogen of TsDPEN, was synthesized using a very simple procedure. The Ru-catalyzed asymmetric transfer hydrogenation of various aromatic ketones in water was investigated with this chiral ligand. High chemical yields and enantioselectivities were obtained under very mild conditions. In addition, the chiral ligand was easily recycled several times and this catalyst was especially suitable for the preparation of chiral tetrahydronaphthalen-1-ol and 2,3-dihydro-1H-inden-1-ol (up to 98% conversion with 99% ee). The latter product can be used as the key intermediate for the synthesis of neuroprotective and anti-AChE agents Rasagiline and Ladostigil.