Dimethyl Sulfoxide and N‑Iodosuccinimide Promoted 5-exo-dig Oxidative Cyclization of Yne-Tethered Ynamide: Access to Pyrrolidones and Spiro-pyrrolidones

An unprecedented metal-free dimethyl sulfoxide (DMSO) and N-iodosuccinimide mediated regioselective 5-exo-dig oxidative cyclization of an in situ generated enol equivalent of amides from ynamides bearing internal alkynes is demonstrated. The reaction allows easy access to functionalized pyrrolidone skeletons. Pyrrolidones having 3-o-biaryl motifs successfully undergo intramolecular electrophilic cyclization with the α,β-unsaturated olefin, furnishing spiro-pyrrolidone motifs. A one-pot sequential 5-exo-dig cyclization of the yne-tethered ynamides, followed by electrophilic cyclization of the pyrrolidone, is presented. The role of DMSO in the transformation is clarified, and a tentative reaction pathway is proposed.