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

Abstract

Abstractα‐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.magnified image