In-Catalyzed Regioselective [3+2] Cycloaddition of Alkenes with α,β-Unsaturated Keto-Carboxylic Acid Derivatives for the Synthesis of γ-Butyrolactones

Herein, we report In(OTf)₃-catalyzed activation of α,β-unsaturated keto-carboxylic acid/ester and successive regioselective (3+2) cycloaddition with alkene to afford diverse new γ-butyrolactone derivatives in very good yields. This expedient strategy is also applicable to α,β-unsaturated amido ester to form various C₃-butyrolactone-substituted oxindole derivatives in very good yields. Mechanistic studies reveal initial activation of the ketone functionality by an In catalyst as the key role to obtain the regioselectivity.