Synthesis of 6-substituted tetrahydropyridinones and cyclization to indolizidine and quinolizidine structures

3-Sulfolenes 1 with various substituents at C-2 underwent [4+2] cycloaddition reactions with p-toluenesulfonyl isocyanate to give the teterahydropyridinones 4. Through N-detosylation and Hg(II)-mediated electrophilic addition/intramolecular cyclization of 4e and 4f, the indolizidine and quinolizidine compounds 7a/7b and 8 were synthesized, respectively.