Diastereo‐ and Enantioselective Synthesis of Chiral Pyrrolidine‐Fused Spirooxindoles via Organocatalytic [3+2] 1,3‐Dipolar Cycloaddition of Azomethine Ylides with Maleimides

In the presence of a Cinchona alkaloid‐based squaramide organocatalyst, the [3+2] cycloaddition of isatin‐derived azomethine ylides with maleimides proceeded readily, thus delivering the desired pyrrolidine‐fused spirooxindoles in 61–89% yields with >20:1 dr and 12 to >99 % ee . The absolute configuration of 5‐chloro‐1,5′‐dimethyl‐3′‐phenyl‐3′,3a′‐dihydro‐2′ H ‐spiro[indoline‐3,1′‐pyrrolo[3,4‐ c ]pyrrole]‐2,4′,6′(5′ H ,6a′ H )‐trione was unambiguously determined by means of X‐ray single crystal structure analysis. The reaction mechanism was hypothesized to account for the enantioselective formation of 5‐chloro‐1,5′‐dimethyl‐3′‐phenyl‐3′,3a′‐dihydro‐2′ H ‐spiro[indoline‐3,1′‐pyrrolo[3,4‐ c ]pyrrole]‐2,4′,6′(5′ H ,6a′ H )‐trione.