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. 2024 Oct 29;10(21):e39911.
doi: 10.1016/j.heliyon.2024.e39911. eCollection 2024 Nov 15.

Chiral amido-oxazoline functionalized MCM-41: A sustainable heterogeneous catalyst for enantioselective Kharasch-Sosnovsky and Henry reactions

Niloofar Tavakoli  1 , Hamid Arvinnezhad  2 , Shiva Majidian  2 , Mahsa Mahramasrar  2 , Khosrow Jadidi  1 , Saadi Samadi  2
Affiliations

Chiral amido-oxazoline functionalized MCM-41: A sustainable heterogeneous catalyst for enantioselective Kharasch-Sosnovsky and Henry reactions

Niloofar Tavakoli et al. Heliyon. .

Abstract

In this study, a series of chiral amido-oxazoline ligands was synthesized with a primary focus on immobilizing the most effective ligands on MCM-41 mesoporous material. Following several attempts, the para-nitro group of the chiral amido-oxazoline ligands was successfully reduced to amino group, enabling their immobilization on MCM-41. The resulting chiral heterogeneous amido-oxazoline ligands were characterized using various techniques, including FT-IR, XRD, TGA, SEM, TEM, EDX, and BET-BJH, confirming the successful immobilization of the amido-oxazoline ligands. A comparison of the efficiency of the homogeneous and heterogeneous amido-oxazoline-based ligands in the Kharasch-Sosnovsky and Henry reactions revealed better performance of the heterogeneous ligand. The immobilized amido-oxazoline-copper complexes exhibited remarkable catalytic activity, achieving excellent yields and enantioselectivities (up to 88 % ee) in the Kharasch-Sosnovsky reaction, and delivering excellent yields with moderate enantioselectivities in the Henry reaction. Notably, the Henry reaction proceeded with moderate diastereoselectivity, favoring the syn diastereomer, under solvent-free conditions, highlighting the sustainability of the process. The heterogeneous nature of the catalysts facilitated effortless recovery and efficient reusability.

Keywords: Amido-oxazoline ligands; Enantioselective Henry reaction; Enantioselective Kharasch–Sosnovsky reaction; Mesoporous MCM-41; Sustainable heterogeneous catalyst.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Image 1
Graphical abstract
Scheme 1
Scheme 1
Synthesis of amido-oxazolines 1.
Scheme 2
Scheme 2
Preparation of the protected amido-oxazolines 8 from para-amino benzoic acid through benzoyl chloride.
Scheme 3
Scheme 3
Preparation of the protected amido-oxazolines 8 from para-amino benzoic acid using Appel reagent.
Scheme 4
Scheme 4
Unsuccessful deprotection of Boc group from the protected amido-oxazolines 8.
Scheme 5
Scheme 5
Direct conversion of the nitro group of amido-oxazolines 1 into amino group using H2, Pd/C.
Scheme 6
Scheme 6
Immobilization of the aniline-oxazoline ligands 9 on mesoporous MCM-41.
Fig. 1
Fig. 1
The FT-IR spectra of MCM-41, Cl-MCM-41, and chiral heterogeneous ligands 10.
Fig. 2
Fig. 2
The XRD patterns of MCM-41, Cl-MCM-41, and chiral heterogeneous ligands 10.
Fig. 3
Fig. 3
The TGA of chiral heterogeneous ligands 10.
Fig. 4
Fig. 4
SEM images of MCM-41, Cl-MCM-41, and chiral heterogeneous ligands 10.
Fig. 5
Fig. 5
The EDX spectra of chiral heterogeneous ligands 10.
Fig. 6
Fig. 6
TEM image of chiral heterogeneous ligand 10a.
Fig. 7
Fig. 7
The nitrogen adsorption–desorption isotherms of chiral heterogeneous ligands 10 at 77 K.
Fig. 8
Fig. 8
Pore size distribution curve of chiral heterogeneous ligand 10a.
Fig. 9
Fig. 9
Enantioselective allylic oxidation of cyclohexene using the chiral homogeneous oxazoline-copper(I) complexes.
Fig. 10
Fig. 10
Comparison of the efficiency of the chiral heterogeneous catalysts using different peresters in the enantioselective allylic oxidation of cyclohexene.
Scheme 7
Scheme 7
Proposed mechanism of the enantioselective allylic oxidation of cyclohexene.
Scheme 8
Scheme 8
Plausible mechanism of the enantioselective Henry reaction.
Fig. 11
Fig. 11
Reusability of catalyst 10a in the enantioselective allylic oxidation of cyclohexene.
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