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.