Concise Asymmetric Synthesis of (-)-Halosaline and (2R,9aR)-(+)-2-Hydroxy-Quinolizidine by Ruthenium-Catalyzed Ring-Rearrangement Metathesis

A ruthenium-catalyzed ring opening-ring closing metathesis reaction serves as the key step in the stereoselective synthesis of a new enantiopure 2-substituted-4.5-dehydropiperidine skeleton, a valuable intermediate for the synthesis of piperidine alkaloids (such as halosaline) and of hydroxylated quinolizidines (such as (2R,9aR)-(+)-2-hydroxy-quinolizidine).