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.