Asymmetric synthesis of spiro[oxindole-3,2′-pyrrolidine]s through organocatalytic 1,3-dipolar cycloaddition <i>via</i> cycloreversion of precursor isatinimine homodimers

The chiral amine catalyzed diastereo- and enantioselective [3 + 2] cycloaddition between isatin-derived azomethine ylides and α,β-unsaturated aldehydes was successfully carried out to afford spiro[oxindole-3,2'-pyrrolidine]s. It was anticipated that the formation of azomethine ylides occurred <i>via</i> the cycloreversion of dispirooxindole-imidazolidines, which are precursor imine homodimers, in aqueous solvents.