Synthesis of Highly Functionalized 1,3-Oxathioles via an unusual [4+1] Annulation of α,α’-Dioxothione with 1,2-Diaza-1,3-dienes

The present method provides highly functionalized 1,3-oxathioles through an unusual base-promoted [4+1] annulation between alpha,alpha'-dioxothione, generated in situ from a phthalimide precursor, and 1,2-diaza-1,3-dienes. An intriguing scaffold comprised of spiro-fused oxathiole and pyrazolone components was also obtained in moderate yield