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

The stereoselective reduction of a diastereoisomeric mixture of benzo[ g ]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 S ,4a S ,10a R )-eutomer of the medicinal drug quinagolide. The obtained data paves the way for an easy and practical attainment of chiral 3-substituted octahydrobenzo[ g ]quinolines that are privileged structures in medicinal chemistry. The study of the reduction of a benzo[ g ]octahydroquinolinium ion was examined in detail under different perspectives until we found a viable solution to get an advanced chiral intermediate of (3 S ,4a S ,10a R )-(−)-quinagolide as a single stereoisomer.