α-Keto Thioesters as Building Blocks for Accessing γ-Hydroxybutenolides and Oxazoles

α-Keto thioesters, with two electrophilic carbon centres, have been found to react differently with β-keto esters and isocyanoacetates. They undergo base induced Knoevenagel-type condensation on the keto carbonyl group with β-keto esters, followed by intramolecular cyclization and water addition leads to highly substituted γ-hydroxybutenolides. On the other hand, substituted oxazole derivatives have been obtained using isocyanoacetates via nucleophilic displacement on the thioester carbonyl followed by intramolecular cyclization. Further functionalization of the γ-hydroxybutenolides is also demonstrated via a BF₃.OEt₂-mediated cation-driven nucleophilic addition of terminal alkynes to access multiply substituted butenolides. (Figure presented.).