Cu(I)-Catalyzed Asymmetric α-Allenylation of Activated Ketimines with 3-Butynoates

Asymmetric aza-Henry reaction toward trifluoromethyl β-nitroamines and biological investigation of their adamantane-type derivatives

Amino acid-derived quaternary ammonium salts were successfully applied in the asymmetric aza-Henry reaction of nitromethane to N-Boc trifluoromethyl ketimines. α-Trifluoromethyl β-nitroamines were synthesized in good to excellent yields with moderate to good enantioselectivities. This reaction is distinguished by its mild conditions, low catalyst loading (1 mol%), and catalytic base. It also proceeded on a gram scale without loss of enantioselectivity. The products were transformed to a series of adamantane-type compounds containing chiral trifluoromethylamine fragments. The potent anticancer activities of these compounds against liver cancer HepG2 and melanoma B16F10 were evaluated. Six promising compounds with notable efficacy have potential for further development.

Visible-Light-Driven C,N-Selective Heteroarylation of N-Fluoroalkyl Hydroxylamine Reagents with Quinoxalin-2(1H)-ones

Herein, we disclose a direct and powerful strategy for the synthesis of highly valuable α-trifluoromethylamine and N-trifluoroethylamine derivatives from a visible-light-promoted C,N-selective heteroarylation of N-trifluoroethyl hydroxylamine reagents with quinoxalin-2(1H)-ones under ambient conditions. The chemoselectivity of the process (trifluoroalkylation or N-trifluoroethylamination) can easily be dictated and modulated by a selection of N-trifluoroethyl hydroxylamine substrates. The key to success is the protecting group on the N atom of hydroxylamine reagents, which can control the process of 1,2-H shift of the in situ-generated N-trifluoroethyl radical. Remarkable features of this method include mild conditions, easy operation, high selectivity, and excellent functional group tolerability. More importantly, the trifluoroalkylated products can be readily derivatized into other interesting imidazo-fused heterocycles that would be of great potential for the exploitation of pharmaceutically relevant molecules.

Amide phosphonium salt catalyzed enantioselective Mannich addition of isoxazole-based nucleophiles to β,γ-alkynyl-α-ketimino esters

An enantioselective Mannich addition of 3,5-disubstituted 4-nitroisoxazoles to β,γ-alkynyl-α-ketimino esters promoted by an amide phosphonium salt-based catalyst has been developed. N-Cbz-protected ketimino esters with various aryl substituents attached to the alkyne unit were reacted with a series of isoxazoles with different substitution patterns. Chiral tertiary propargylic amine products were obtained with moderate to good yields and enantioselectivities. TIPS- and cyclopropyl-substituted alkynyl ketimines were also examined in the current system and the desired products were obtained with moderate yields and enantioselectivities. The potential scalability and utility of the current protocol were demonstrated by carrying out a relatively larger scale reaction followed by further transformations.

Recent advances in the applications of pyrazolone derivatives in enantioselective synthesis

Pyrazolones and pyrazoles, featuring nitrogen-nitrogen bonds, are two of the most important classes of heterocycles, owing to their widespread occurrence in medicinal chemistry and functional materials. The last decade has witnessed a rapid increase in the construction of chiral pyrazolone and pyrazole derivatives, with the application of pyrazolone derivatives as powerful synthons. Since our last review in 2018, a large number of new achievements has emerged in this area, requiring a timely update. Thus, this review summarizes these elegant achievements based on the multiple reactive sites of different pyrazolone synthons. In addition, important mechanisms and interesting biological investigations relating to the corresponding products are also discussed.

Asymmetric Catalytic Ketimine Mannich Reactions and Related Transformations

The catalytic enantioselective ketimine Mannich and its related reactions provide direct access to chiral building blocks bearing an α-tertiary amine stereogenic center, a ubiquitous structural motif in nature. Although ketimines are often viewed as challenging electrophiles, various approaches/strategies to circumvent or overcome the adverse properties of ketimines have been developed for these transformations. This review showcases the selected examples that highlight the benefits and utilities of various ketimines and remaining challenges associated with them in the context of Mannich, allylation, and aza-Morita-Baylis-Hillman reactions as well as their variants.

Regio- and enantioselective amination of acyclic branched α-alkynyl ketones: asymmetric construction of N-containing quaternary stereocenters

Direct regio- and enantioselective amination of acyclic α-branched ketones enabled by the α-alkynyl group.

Palladium-catalysed oxidative nucleophilic allylation between alkenes and activated ketimines

A direct linear regioselective oxidative allylation reaction between alkenes and activated ketimines has been developed by using a Pd(OAc)2/2,6-dimethyl-1,4-benzoquinone system.

Catalytic enantioselective synthesis of chiral 4-hydroxy 4′-substituted pyrazolones by the vinylogous aldol reaction of pyrazole-4,5-diones with 3-alkylidene-2-oxindoles

Here, a bifunctional quinine-derived benzamide catalyzed direct enantioselective vinylogous aldol reaction between 3-alkylidene-2-oxindoles and pyrazole-4,5-diones has been developed.

Strategies for the Catalytic Enantioselective Synthesis of α-Trifluoromethyl Amines

The exploitation of the α-trifluoromethylamino group as an amide surrogate in peptidomimetics and drug candidates has been on the rise. In a large number of these cases, this moiety bears stereochemistry with the stereochemical identity having important consequences on numerous molecular properties, such as the potency of the compound. Yet, the majority of stereoselective syntheses of α-CF₃ amines rely on diastereoselective couplings with chiral reagents. Concurrent with the rapid expansion of fluorine into pharmaceuticals has been the development of catalytic enantioselective means of preparing α-trifluoromethyl amines. In this work, we outline the strategies that have been employed for accessing these enantioenriched amines, including normal polarity approaches and several recent developments in imine umpolung transformations.

Recent Advances in Catalytic Enantioselective Synthesis of Pyrazolones with a Tetrasubstituted Stereogenic Center at the 4-Position

Pyrazolone [2,4-dihydro-3H-pyrazol-4-one] represents one of the most important five-membered nitrogen heterocycles which is present in numerous pharmaceutical drugs and molecules with biological activity. Recently, many catalytic methodologies for the asymmetric synthesis of chiral pyrazolones have been established with great success, specially, for the synthesis of pyrazolones bearing a tetrasubstituted stereocenter at C-4. This review summarizes these excellent research studies since 2018, including representative examples and some mechanistic pathways explaining the observed stereochemistry.

1 Introduction

2 Catalytic Enantioselective Synthesis of Chiral Pyrazolones with a Full Carbon Tetrasubstituted Stereocenter at C-4

3 Catalytic Enantioselective Synthesis of Chiral Pyrazolones with a Quaternary Carbon Stereocenter at C-4 bearing a Heteroatom

4 Catalytic Enantioselective Synthesis of Chiral Spiropyrazolones

5 Conclusion