Catalytic Asymmetric Synthesis of Thiols

The synthesis of enantio­pure thiols is of significant interest for industrial and academic applications. However, direct asymmetric approaches to free thiols have previously been unknown. Here we describe a novel organo­cascade that is catalyzed by a confined chiral phosphoric acid and furnishes <i>O</i>-protected β-hydroxy­thiols with excellent enantio­selectivities. The method relies on an asymmetric thio­carboxylysis of <i>meso-</i>epoxides, followed by an intra­molecular <i>trans</i>-esterification reaction. By varying the reaction conditions, the intermediate thioesters can also be obtained chemo­selectively and enantio­selectively