Thiourea–Quaternary Ammonium Salt Catalyzed Asymmetric 1, 3‑Dipolar Cycloaddition of Imino Esters To Construct Spiro[pyrrolidin-3,3′-oxindoles]

A highly enantioselective 1,3-dipolar cycloaddition of imino esters with methyleneindolinones has been realized by using readily available thiourea–quaternary ammonium salts as phase-transfer catalysts, enabling efficient construction of a range of chiral spiro­[pyrrolidin-3,3′-oxindoles] in good yields with excellent enantioselectivities under mild conditions.