Showing papers by "Liu-Zhu Gong published in 2019"
TL;DR: Both reactions represent a nicely synergistic integration of NHC carbene and copper catalysis, in which each catalyst activates the substrates, respectively, and the chiral NHC perfectly controls the stereochemistry.
Abstract: Highly enantioselective [3+3] and [3+4] annulations of isatin-derived enals with ethynylethylene carbonates and ethynyl benzoxazinanones are enabled by NHC/cooper cooperative catalysis, leading to a big library of spirooxindole derivatives in high structural diversity and enantioselectivity (up to 99 % ee). Both reactions represent a nicely synergistic integration of NHC and copper catalysis, in which both catalysts activate the substrates and the chiral NHC perfectly controls the stereochemistry.
118 citations
TL;DR: In this paper, a review summarizes typical advances on Pd(0)-catalyzed difunctionalization of 1,3-dienes in recent decades, particularly emphasizing the concepts that enable the switch from a racemic reaction to an enanti-lective version.
Abstract: 1,3-Dienes are easily accessible chemicals that participate in a series of reactions acting on the carbon–carbon double bonds. Catalytic difunctionalization of 1,3-dienes provides a wide scope of functionalized chemicals. Pd(0) catalysts provide a diverse set of principles for the creation of asymmetric catalytic reactions, which are initiated with the oxidative addition and then undergo insertion reaction with one of double bonds of the 1,3-diene to become a π-allyl palladium species that is reactive toward nucleophilic attack. This review summarizes typical advances on the Pd(0)-catalyzed difunctionalization of 1,3-dienes in recent decades, particularly emphasizing the concepts that enable the switch from a racemic reaction to an enantioselective version. 1 Introduction 2 Amination 3 Boration 4 Carbonation 5 Hydrogenation 6 Oxygenation 7 Silylation 8 Conclusion and Outlook
79 citations
TL;DR: Experimental and computational studies on the reaction mechanism suggest a novel concerted proton and two-electron transfer process for the allylic C-H cleavage and reveal that the Z/ E- and regioselectivities are governed by the geometry and coordination pattern of nucleophiles.
Abstract: The asymmetric allylic alkylation (AAA), which features employing active allylic substrates, has historical significance in organic synthesis. The allylic C–H alkylation is principally more atom- a...
77 citations
TL;DR: The combination of a commercially available Pd(II) catalyst and diphenylprolinol was able to provide the γ-addition products with good to high yields and efficient stereochemical control (up to 95% ee).
Abstract: Amine/Pd(II) cooperative catalysis has enabled a highly enantioselective addition of cyclic ketones to unactivated alkenes. The hallmark of the strategy includes amide-directed, regioselective activation of alkenes by Pd(II) and enhancing the nucleophilicity of α-carbon of the ketones by enamine catalysis to synergistically drive the reaction, which is basically unable to be accessed by a single catalyst. The combination of a commercially available Pd(II) catalyst and diphenylprolinol was able to provide the γ-addition products with good to high yields and efficient stereochemical control (up to 95% ee).
58 citations
TL;DR: Mechanistic investigations have revealed the nature of the C-H activation and the origin of the enantioselectivity and significant synergy between the chiral ligand and the anion in terms of stereochemical control was observed.
Abstract: An unusual hybrid palladium catalyst containing an anionic chiral CoIII complex and a chiral phosphoramidite ligand shows a high capacity for catalyzing asymmetric thioamide-directed C(sp3 )-H arylation and delivers excellent yield and enantioselectivity (up to 99 % yield, 99 % ee). Significant synergy between the chiral ligand and the anion in terms of stereochemical control was observed. Mechanistic investigations have revealed both the nature of the C-H activation and the origin of the enantioselectivity.
54 citations
TL;DR: An asymmetric allylic C-H alkylation of allyl ethers has been established by chiral phosphoramidite-palladium catalysis, affording a wide variety of functionalized chiral 2-acylimidazoles in moderate to high yields and with high levels of enantioselectivity.
Abstract: An asymmetric allylic C-H alkylation of allyl ethers has been established by chiral phosphoramidite-palladium catalysis, affording a wide variety of functionalized chiral 2-acylimidazoles in moderate to high yields and with high levels of enantioselectivity. Moreover, this protocol could be applied to a concise asymmetric synthesis of a tachykinin receptor antagonist.
46 citations
TL;DR: A general strategy for the design of asymmetric cascade reactions using readily available halides and carbon monoxide (CO) as substrates is developed and asymmetric formal [1+1+4] and [1-1+2] reactions are established to afford chiral dihydropyridones and β-lactams with high yields and high enantio- and diastereoselectivities.
Abstract: A general strategy for the design of asymmetric cascade reactions using readily available halides and carbon monoxide (CO) as substrates is developed. The key is the catalytic generation of C1-ammonium enolates for the subsequent asymmetric cascade reactions through the combination of palladium-catalyzed carbonylation and chiral Lewis base catalysis. Utilizing this strategy, we have established asymmetric formal [1+1+4] and [1+1+2] reactions to afford chiral dihydropyridones and β-lactams with high yields and high enantio- and diastereoselectivities.
40 citations
TL;DR: Mechanistic studies suggest that a ternary Pd(0) complex, coordinated with a monodentate phosphorus ligand, benzoquinone, and alkene, is most likely to be an active species.
35 citations
TL;DR: Mechanistic studies by density functional theory (DFT) calculations suggest a nucleophile coordination-enabled inner-sphere attack mode for the enantioselective carbon-carbon bond-forming event.
Abstract: Branched selectivity in asymmetric allylic C-H alkylation is enabled by using 2-acylimidazoles as nucleophiles in the presence of a chiral phosphoramidite-palladium catalyst. A wide range of terminal alkenes, including 1,4-dienes and allylarenes, are nicely tolerated and provide chiral 2-acylimidazoles in moderate to high yields and with high levels of regio-, and enantio-, and E/Z-selectivities. Mechanistic studies using density-functional theory calculations suggest a nucleophile-coordination-enabled inner-sphere attack mode for the enantioselective carbon-carbon bond-forming event.
34 citations
TL;DR: The first Pd(II)-catalyzed asymmetric oxidative annulation of N-alkoxyaryl amides and 1,3-dienes is reported, which features particular applicability for quick assembly of different types of chiral heterocycles with high yields and enantioselectivities.
29 citations
TL;DR: An enantioselective catalytic alkoxylation/oxidative rearrangement of allylic alcohols has been established by using a Brønsted acid and chiral organoiodine to create enantioenriched α-arylated β-alkoxylated ketones.
Abstract: An enantioselective catalytic alkoxylation/oxidative rearrangement of allylic alcohols has been established by using a Bronsted acid and chiral organoiodine. The presence of 20 mol % of an (S)-proline-derived C2 -symmetric chiral iodine led to enantioenriched α-arylated β-alkoxylated ketones in good yields and with high levels of enantioselectivity (84-94 % ee).
TL;DR: In the presence of chiral phosphoramidite ligand, a palladium-catalyzed asymmetric allylic C-H alkylation of 1,4-dienes with cyclic β-keto esters has been established to afford chiral α,α-disubstit...
TL;DR: This work described a chiral aldehyde-catalyzed biomimetic Mannich reaction of tert-butyl glycine ester hydrochloride and N-diphenylphosphinyl imine, a significant leap forward in asymmetric carbonyl catalysis.
Abstract: Asymmetric organocatalysis has been a robust tool for manufacturing optically active molecules, in addition to asymmetric metal and biocatalysis [1]. The development of new concepts and catalysts to enable the creation of efficient synthetic methods has been a longstanding activity in this field. During the last decades, a diverse spectrum of chiral organocatalysts, including ketones, amine, Brønsted acids and bases, phase-transfer catalysts, and nucleophilic catalysts, have been developed, culminating in a large number of transformations enabling the efficient construction of optically active natural and unnatural compounds. Despite of these great achievements, the asymmetric direct α-functionalization of N-unprotected amines, which offers a very straightforward approach to access chiral amine compounds, is very hard to be realized by virtue of commonly available organocatalytic concepts. It is well known that the α-C–H bond of an amine can be activated by an aldehyde via the formation of an imine. Importantly, the imine formation is basically reversible to thereby allow chiral aldehydes to be promising organocatalysts for the direct α-functionalization of N-unprotected amines. Nature has already pointed out this possibility [2], however, the mimic of nature to design artificial chiral aldehyde catalysts and asymmetric processes has not gained breakthroughs, until recently [3,4]. In fact, the chiral aldehyde catalysis can be traced back to the middle of last century. For example, chiral pyridoxaldependent enzyme catalysis has been successfully used in the aldol reaction of amino acids with aldehydes, a biological process involved in amino acid metabolism [2]. Inspired by this process, several biomimetic chiral pyridoxal analogues have been designed, however, they are unable to give satisfactory chiral induction for reactions other than the aldol reaction. In 2011, Beauchemin and coworkers [5] indicated that the chiral glyceraldehyde analogues turned out to be good catalysts for intermolecular Cope-type hydroaminations of allylic amines. In 2014, the chiral aldehyde catalysis by using imine activation concept was first proposed by Guo et al. [3], leading to a chiral BINOL-derived aldehyde-catalyzed direct asymmetric α-alkylation of 2-aminomalonate (Figure 1(a)). Very recently, the chiral aldehyde catalysis based on imine activation principle gained a significant breakthrough. Zhao, Yuan and co-workers [4] described a chiral aldehyde-catalyzed biomimetic Mannich reaction of tert-butyl glycine ester hydrochloride and N-diphenylphosphinyl imine. A new type of chiral pyridoxal analogues containing a chiral axis and carbon stereogenic centers were designed and exploited as bifunctional catalysts to allow the direct asymmetric Mannich reaction proceeding with high levels of enantioselectivity. In fact, the scope of chiral pyridoxal catalysis has been limited to the asymmetric aldol reaction for half century. As such, this work represents a significant leap forward in asymmetric carbonyl catalysis. Moreover, the use of readily available amino esters greatly enhances the practical application of this reaction for the preparation of unnatural chiral amino acids. Even more significantly, the efficiency of