Theoretical and experimental studies on the structure–property relationship of chiral N,N′-dioxide–metal catalysts probed by the carbonyl–ene reaction of isatin

Abstract

Variation of the linkage or chiral backbone of an N,N′-dioxide ligand adjusts the blocking effect of ortho-iPr on the reaction site, affecting the enantiodifferentiation of two competing pathways.

Theoretical Study on Asymmetric [2 + 2] Cycloaddition of an Alkynone with a Cyclic Enol Silyl Ether Catalyzed by a Chiral N,N′-Dioxide-Zn(II) Complex

“…The mechanism of cycloaddition between an alkynone (R1) and a cyclic enol silyl ether (R2) mediated by a chiral N,N ′-dioxide-Zn­(II) complex (CAT) was further studied at the same theoretical level. On the basis of the X-ray crystal structure of the N,N ′-dioxide-Zn­(II) , complex and our previous works, − a hexacoordinate Zn­(II) complex was considered to be an active species. We first focused on the Zn­(II) complex containing a chiral N,N ′-dioxide ligand L2 with two CH 2 groups in the linkage (see Scheme , m = 1), which was reported in experiments .…”

“…Our previous studies indicated that a counterion could coordinate to the metal center of a chiral N , N ′-dioxide-metal complex, stabilizing the active species, adjusting the Lewis acidity of the metal center, and even taking part in reactions . The positive effect of the counterion NTf 2 – in alkenylsilylation reactions was also studied by Xia and co-workers. , To understand the role of the counterion NTf 2 – in [2 + 2] cycloaddition reactions, we also optimized the geometry of a pentacoordinate Zn­(II) complex without an NTf 2 – anion (L2-COM-P).…”

“…Role of Counterion NTf 2 − . Our previous studies indicated that a counterion could coordinate to the metal center of a chiral N,N′-dioxide-metal complex, stabilizing the active species, 38 adjusting the Lewis acidity of the metal center, 39 and even taking part in reactions. 43 The positive effect of the counterion NTf 2 − in alkenylsilylation reactions was also studied by Xia and co-workers.…”

Heteroaromatic N-Oxides in Asymmetric Catalysis: A Review

“…Enantiomeric excess up to 83% and yield up to 97% were achieved. Currently, rather the applications of chiral alkyl amine N-oxides (mostly proline N-oxide derivatives) as ligands for metal complexes, in various types of asymmetric reactions, can be found in the literature [64][65][66]. The different direction was presented by Wolińska, who used chiral pyridine N-oxide derivatives possessing oxazoline moiety 49-51 (see Figure 10) for the asymmetric nitroaldol reaction, catalyzed by a copper complex.…”

Asymmetric Baeyer–Villiger oxidation: classical and parallel kinetic resolution of 3-substituted cyclohexanones and desymmetrization of meso-disubstituted cycloketones

“…The induced-fit model of BV oxidation in biocatalysis provides such a sight of view for molecular catalysts that a conformationally flexible structure can streamline the adjustment of catalysts toward cycloketones with different configurations and conformations, leading to high regio- and stereo-selectivity 4d,4f,7c,10. The privileged chiral N , N ′-dioxide, bearing a catenulate alkyl linker as well as two backbones and aniline groups bound to Lewis acids, is by nature a flexible structure,11 which forms an adjustable blocker for chiral recognition. Herein, we describe novel CKR, PKR and desymmetrization of 3-substituted cycloketones (non-functional group) with a single chiral N , N ′-dioxide/Sc( iii ) catalytic system (Scheme 1b).…”