The First Enantioselective Organocatalytic Synthesis of 3-Spiro-α-Alkylidene-γ-Butyrolactone Oxindoles

Abstract

A new and flexible methodology catalyzed by bifunctional chiral thioureas has been developed to react β-nitro oxindoles 1 with aldehydes. This approach allowed us to achieve the first enantioselective organocatalytic synthesis of 3-spiro-α-alkylidene-γ-butyrolactone oxindoles 3. We examined the scope of the two starting materials and, varying the structure of the β-nitro oxindole 1, intriguing new products, derived from unexpected transformations, have been stereoselectively obtained. The aim of this study was to merge two potentially bioactive structural motifs: the spirooxindole substructure and the α-alkylidene-γ-butyrolactone moiety. A preliminary NMR study on the ability to reversibly trap 2-aminoethanethiol gave us promising results.

Keywords: bifunctional thioureas; lactones; organocatalysis; oxindoles; spiro compounds.