Fused and Spirocyclic Sulfones for Medicinal Chemistry via [3 + 2] Cycloaddition of Thiocarbonyl Ylide

The [3 + 2] cycloaddition between thiocarbonyl ylide CH₂═S⁽⁺⁾–CH₂⁽⁻⁾ and electron-deficient cyclic alkenes provides bicyclic sulfides. The reaction efficiently works on milligram, gram, and even multigram quantities. Standard modifications of the obtained products give fused and spirocyclic sulfones for medicinal chemistry.