N‐Heterocyclic Carbene‐Catalyzed Atroposelective Annulation for Access to Thiazine Derivatives with C−N Axial Chirality

Abstract A catalytic atroposelective cycloaddition reaction between thioureas and ynals is developed. This reaction features the first NHC‐catalyzed addition of thioureas to acetylenic acylazolium intermediates to eventually set up C−N axial chirality with excellent optical purities. The obtained axially chiral thiazine derivative products bear multiple functional groups and are feasible for further transformations.