Synthesis and transformations of sulfur-substituted indolizidines and quinolizidines

3-Sulfolenes 1a–b underwent [4+2] cycloaddition reactions with p-toluenesulfonyl isocyanate to give tetrahydropyridinones 3a–b. Through N-detosylation of 3a–b and subsequent intramolecular cyclization, indolizidine 5a and quinolizidine 5b were synthesized. Useful functional group transformations of compounds 5a–b were also investigated.