Solvent-free Mukaiyama-aldol condensation catalyzed by Ce–Al–MCM-41 mesoporous materials

MCM-41 samples containing Ce4+ and Al3+ in the network, designated as Cex–Al–MCM-41 (x = 0.0–0.04), were synthesized and characterized systematically. These samples exhibited higher catalytic activity for Mukaiyama-aldol condensations to produce β-hydroxy carbonyl compounds under the solvent free conditions, compared to the samples containing either of the two cations. The product yield was found to depend on the electron donating/withdrawing characteristics of reactant molecules being responsible for the observed trend. Series of solvents were also investigated but considerably high yield of aldol products (∼95%) could be achieved without using any solvents. In all the cases, the selectivity was found to be 100%, typical of such Mukaiyama-aldol condensations. The higher catalytic activity of Cex–Al–MCM-41 is explained on the basis of certain new acid sites generated due to co-incorporation of Ce and Al cations.

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► Ce–Al–MCM-41.
► Acid catalyst.
► Silyl ketene acetal.
► Silyl enol ether and aldehyde.