Synthesis of spiropyrrolidine oxindoles via Ag-catalyzed stereo- and regioselective 1,3-dipolar cycloaddition of indole-based azomethine ylides with chalcones
The synthesis of novel spiropyrrolidine oxindole derivatives was reported, using Ag-catalyzed [3+2] cycloaddition of azomethine ylides generated in situ from the condensation of substituted isatins and primary α-amino acid esters with chalcones. Products bearing four consecutive stereocenters, including spiroquaternary stereocenters fused in one ring structure, were smoothly acquired in moderate to high yields (50–95%) with good to excellent diastereoselectivities (11 : 1 → 20 : 1 dr). Furthermore, product 4a underwent reduction, oxidation, hydrolysis and amidization to give the corresponding alcohol, dihydropyrrole, pyrrole, acid and amide, respectively, in good yields. The synthesized compounds (>100 examples) were well characterized through different spectroscopic techniques, such as single crystal XRD, FTIR, NMR, and mass spectral analysis.