Synthesis of Extended Bipyridine‐proline Chiral Catalysts and Resulting Effects on the Asymmetric Aldol Reactions of Bulkier Aldehyde Derivatives with Cyclohexanone. Issue 35 (16th September 2020)

• Record Type: Journal Article
• Authors: Xu, Guangpeng; Zhang, Yajing; Sun, Jihong; Bai, Shiyang; Zhao, Hongwu
• Is Part Of: ChemistrySelect. Volume 5:Issue 35(2020)
• Page Start: 10996
• Page End: 11003
• Publication Date: 2020-09-16
• Subjects: Aldehydes -- Asymmetric catalysis -- Bipyridine-proline derivatives -- Diastereoselectivity -- Solvent effects; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/slct.202002956
• Languages: English
• ISSNs: 2365-6549

Abstract

Abstract: Axially‐unfixed 2, 2′‐bipyridine‐based chiral catalysts were synthesized using enantiopure amino acids as chiral sources, which were successfully used in asymmetric aldol reactions of p ‐nitrobenzaldehyde with cyclohexanone, while the bulkier aldehyde derivatives (2‐naphthaldehyde, 9‐anthracenecarboxaldehyde, and 1‐pyrenecarboxaldehyde) were selected to further elucidate the catalytic properties. Particularly, the influences of the bipyridine‐proline chiral structures and the polarities of used solvents (petroleum ether, toluene, CH2 Cl2, ethanol, DMF, DMSO, and water) on the catalytic performance were investigated. The results indicated that the structure of bipyridine catalysts, the molecular volume of aldehydes, and the polarity of solvents have significant effects on the catalytic activities, in which, the smaller steric effects were conducive to the improvement of the yields and stereoselectivities for asymmetric aldol reaction, along with the increased polarity of used solvents and the decreased molecular volume of aldehydes. Meanwhile, the chemical identity of all compounds was confirmed by 1 H‐NMR, 13 C‐NMR, HRMS, and HPLC analysis. Abstract : The organocatalysts of bipyridine‐proline were prepared, and the influences of various polar solvents and the bulkier aldehyde derivatives on the asymmetric aldol reaction performances were elucidated. Under the optimal reaction conditions, one organocatalyst in particular delivered high efficiency (yield of about 96 %) and good stereocontrol (up to 41 % ee and 78 : 22 dr ) in DMSO media.