Dual stereocontrolled alkylation of aldehydes with polystyrene-supported nickel complexes derived from α-amino amides

Abstract

Nickel(II) complexes derived from a-amino amide ligands anchored to gel-type and monolithic polymers act as efficient catalysts for the enantioselective addition of dialkylzinc reagents to aldehydes. Similar to the analogous homogeneous systems, dual stereocontrol in addition products can be achieved by controlling the stoichiometry of the immobilized nickel complex. Aromatic and aliphatic aldehydes were alkylated in good yields with enantioselectivities comparable to those obtained with the homogeneous analogues. These polymer-supported catalysts offer significant advantages as no metal leaching is observed and they can be easily recovered from the reaction mixture by simple filtration and reused for subsequent experiments with consistent catalytic activity.

Chiral catalysts immobilized on achiral polymers: effect of the polymer support on the performance of the catalyst

“…The possibility of site isolation or preconcentration of the catalytic sites as a function of polymer structure and morphology has also been exploited to achieve a dual stereocontrol in the case of supported amino amides that are able to provide the two enantiomers for the Ni(II) catalysed Et 2 Zn addition to aldehydes depending on the ligand : metal ratio. 390,391 Schurig and coworkers had also reported a reversal in enantioselectivity upon immobilization for the hetero-Diels-Alder reaction between trans-1-methoxy-3-trimethylsiloxy-1,3-butadiene (343) and benzaldehyde catalysed by an oxovanadium complex (Fig. 82).…”