Enantioselective Synthesis of 3-Acetyl Coumarin Substituted 3-Hydroxy Oxindoles and Pyranocoumarin Fused Spirooxindoles

Enantioselective construction of bioinspired coumarin and oxindole hybrid structures always enduring challenges in organic chemistry due to the generation of asymmetric quaternary/spiro center at the C3 position of oxindole. Herein, we demonstrated a facile enantioselective synthesis of highly functionalized 3,3’-disubstituted oxindole derivatives containing 3-acetyl coumarins and pyranocoumarin fused spirooxindoles using L-proline derived bifunctional thiourea organocatalyst through Aldol reaction and Michael addition/cyclization. The L-proline derived thiourea catalyst well performed with broad substrate scope to produce desired products in very good yields (up to 95 %) and excellent enantioselectivities (up to 99 % ee).