Lanthanum-pyBOX complexes as catalysts for the enantioselective conjugate addition of malonate esters to β,γ-unsaturated α-ketimino esters

4Citations
Citations of this article
5Readers
Mendeley users who have this article in their library.
Get full text

Abstract

In this paper, we report the application of chiral complexes of La(III) with pyBOX ligands as Lewis acid catalysts in the conjugate addition of malonic esters to N-tosyl imines derived from β,γ-unsaturated α-keto esters to give the corresponding chiral α,β-dehydroamino esters. pyBOX complexes with La(III), Yb(III), Sc(III), and In(III) triflates were assessed in this reaction but only La(III) showed good activity and enantioselectivity, while Yb(III) provided the expected product with low yield and stereoselectivity, and the Sc(III) and In(III) complexes were completely inactive. The complex of La(OTf)3 with the diphenyl-pyBOX ligand prepared in situ provided the best results and allowed obtaining chiral α,β-dehydroamino esters 3 with excellent yields, E:Z diastereomeric ratios (29:71–99:1) and high enantiomeric excesses (20–95%). The reaction could be applied to imines having a substituted aromatic ring or a heterocycle attached to the double bond, although the presence of electron-withdrawing groups on the aromatic ring was detrimental for stereoselectivity. The reaction products were obtained with the S configuration at the stereogenic center and the Z configuration at the enamine double bond as determined by NOESY experiments and X-ray analysis. Based on the experimental results a stereochemical model involving a nine-coordinate La(III) species has been proposed.

Cite

CITATION STYLE

APA

Espinosa, M., Blay, G., Cardona, L., Fernández, I., Muñoz, M. C., & Pedro, J. R. (2018). Lanthanum-pyBOX complexes as catalysts for the enantioselective conjugate addition of malonate esters to β,γ-unsaturated α-ketimino esters. Journal of Coordination Chemistry, 71(6), 864–873. https://doi.org/10.1080/00958972.2018.1437422

Register to see more suggestions

Mendeley helps you to discover research relevant for your work.

Already have an account?

Save time finding and organizing research with Mendeley

Sign up for free