Selective C3-alkenylation of oxindole with aldehydes using heterogeneous CeO₂ catalyst

We report herein that a commercially available CeO2 is an active and reusable catalyst for the C3-selective alkenylation of oxindole with aldehydes under solvent-free conditions. This. catalytic method is generally applicable to different aromatic and aliphatic aldehydes, giving 3-alkyledene-oxindoles in high yields (87%-99%) and high stereoselectivities (79%-93% to E-isomers). This is the first example of the catalytic synthesis of 3-alkenyl-oxindoles from oxindole and various aliphatic aldehydes. The Lewis acid-base interaction between Lewis acid sites on CeO2 and benzaldehyde was studied by in situ IR. The structure-activity relationship study using CeO2 catalysts with different sizes suggests that defect-free CeO2 surface is the active site for this reaction. (C) 2020, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.