Synthesis of sulfur-substituted quinolizidines and pyrido[1,2-a]azepines by ring-closing metathesis

Sulfur-substituted quinolizidines and pyrido[1,2-a]azepines (7) can be prepared by ring-closing metathesis (RCM) of 4-(phenylthio)-1,2,5,6-tetrahydropyridin-2-ones (6) bearing terminal alkenyl groups at both N-1 and C-6 positions, which are obtained from 3-(phenylthio)-3-sulfolene (1) in four steps. Some synthetic transformations of 2-(phenylthio)-1,6,9,9a-tetrahydroquinolizin-4-one (7a) and 2-(phenylthio)-1,6,9,10,10a-pentahydropyrido[1,2-a]azepin-4-one (7d) are also reported.