One-pot multicomponent diastereoselective synthesis of indoline spirobicyclics using a recyclable chiral nanomagnetic L-proline catalyst under mild conditions

Fe₃O₄@SiO₂-NH-TCT-(trans-4-hydroxy-L-proline)₂ nanoparticles were synthesized as a chiral, magnetically recoverable nanocatalyst. The material was thoroughly characterized by FT-IR, VSM, XRD, TEM, FE-SEM, BET, CHNS elemental analysis, mass spectrometry, and ¹H/¹³C-NMR. The catalyst enabled a one-pot, multicomponent diastereoselective synthesis of indoline spirobicyclic derivatives from anilines, carbon acids, Fischer's base, and aldehydes under solvent-free conditions at ambient temperature. The method afforded high to excellent yields with excellent diastereoselectivity. Product structures and anti/syn diastereomeric ratios were established by ¹H-, ¹³C-NMR, 2D-ROESY, mass spectrometry, and single-crystal X-ray diffraction.