Development of an asymmetric formal synthesis of (-)-quinagolide enzymatic resolution and stereoselective iminium ion reduction.

The stereoselective reduction of a diastereoisomeric mixture of benzo[]octahydroquinolinium ion was examined in detail. A diastereoselective borohydride reduction in combination with an efficient deacylative enzymatic resolution of its β-aminoester precursor are the key steps for a stereoselective installation of the three chiral centres present in the (3,4a,10a)-eutomer of the medicinal drug quinagolide. The obtained data paves the way for an easy and practical attainment of chiral 3-substituted octahydrobenzo[]quinolines that are privileged structures in medicinal chemistry.