Cu(II)-Catalyzed [3+2] Annulation of Thioamides with AIBN: Facile Access to Highly Functionalized Thiazolidine-4-ones

An efficient and versatile copper-catalyzed unprecedented intermolecular radical [3 + 2] annulation of thioamides with azobisisobutyronitrile (AIBN) is described. This two-component one-pot copper(II)-catalyzed transformation has been achieved via cascade formation of C-S/C−N bonds through the cyclization of in situ generated N,S-acetal intermediate from β-ketothioamide. This operationally simple method allows direct access to synthetically demanding thiazolidin-4-ones in good to excellent yields containing diverse functional groups of different electronic and steric nature. Remarkably, the readily available reaction partners, avoidance of expensive/toxic reagents and the gram scale synthesis are additional attributes to this strategy. AIBN here plays a dual role as radical initiator and unusual source of two carbon coupling partner. Notably, the products possess Z-stereochemistry with regard to the exocyclic C=C double bond at the 2-position of the thiazolidine ring.