Metal-Free Aminothiationof Alkynes: Three-ComponentTandem Annulation toward Indolizine Thiones from 2‑Alkylpyridines,Ynals, and Elemental Sulfur

A metal-free three-component annulation reaction for the synthesis of indolizine thiones via tandem C–C/C–N/C–S bond formation was developed. Various 2-alkylpyridines with aromatic ynals and elemental sulfur proceeded smoothly under catalyst-free conditions, and the desired products were obtained in moderate to excellent yields.