Heterogeneous Prolinamide-Catalyzed Atom-Economical Synthesis of β-Thioketones from Bio-Based Enones

Sulfur-containing compounds are a class of important motifs extensively applied in pharmaceutical and pesticidal industries as well as in electrochemistry, toxicant separation, and organic syntheses. Herein, we describe a novel and efficient metal-free catalytic strategy for the rapid synthesis of β-thioketones from sustainable enone derivatives and thiols via thia-Michael addition enabled by heterogeneous prolinamide. At room temperature, up to 98% yield of β-thioketones could be obtained over the solid UiO-66-NH-proline catalyst facilely prepared by the covalent immobilization of proline onto UiO-66-NH₂ (a well-known metal-organic framework) via a stable amido linkage. A cooperative effect of proline (amino group) and UiO-66-NH₂ (in situ-derived amide species) was observed to play a promotional role in the proceeding of thia-Michael addition, resulting in a high TOF value of 1124.3 h^-1. A three-component "iminium" intermediate was illustrated to the key species approaching the product β-thioketone. Moreover, the UiO-66-NH-proline could be easily recovered from the reaction mixture and recycled for at least five times with a slight loss of activity.