Controlled Synthesis of Enantioselective 1-Aminoindenes via Cobalt-Catalyzed [3 + 2] Annulation Reaction

Cobalt-Catalyzed Asymmetric Reductive Alkenylation and Arylation of Heterobiaryl Tosylates: Kinetic Resolution or Dynamic Kinetic Resolution?

Herein, we report a cobalt-catalyzed atroposelective reductive cross-coupling of racemic heterobiaryl tosylates with a C(sp2)-X type electrophile. Both aryl and alkenyl halides are competent precursors for this reaction, providing a variety of heterobiaryls as the products in a highly enantioselective manner with high functionality tolerance. The related asymmetric arylation and alkenylation are discovered to proceed with divergent mechanisms. The reaction pathway changes from kinetic resolution (KR) when alkenyl bromides and aryl iodides bearing strong electron-withdrawing substitution on the para-position are employed as the starting materials to an enantioconvergent transformation via dynamic KR of configurationally labile cobaltacycles when relatively electron-rich aryl iodides are used. The change of the reaction mechanisms turns out to arise from the relative rates of two competing elementary steps, which are the epimerization of the cyclic Co(I) intermediates and their trapping by the coupling electrophiles of the C(sp2)-type via oxidative addition.

Cobalt-Catalyzed Chemo- and Stereoselective Arylative Carbocyclization of 1,6-Allenynes

Different from the well-investigated enynes, transition-metal-catalyzed carbocyclization reactions of allenynes are more attractive as a result of the unique structure and versatile reactivity of allenes. Herein, we report the first cobalt-catalyzed highly chemo- and stereoselective arylative carbocyclization of 1,6-allenynes with arylboronic acids, affording five-membered carbocycles and heterocycles with moderate to high yields, broad substrate scope, and wide functional group compatibility. Moreover, several mechanistic experiments were conducted to gain insight into the reaction process.

Enantioselective Dearomative [3 + 2] Umpolung Annulation of N-Heteroarenes with Alkynes

Enantioselective [3 + 2] annulation of N-heteroarenes with alkynes has been developed via a cobalt-catalyzed dearomative umpolung strategy in the presence of chiral ligand and reducing reagent. A variety of electron-deficient N-heteroarenes, including quinolines, isoquinolines, quinoxaline, and pyridines, and internal or terminal alkynes are employed in this reaction, showing a broad substrate scope and good functionality tolerance. Annulation of electron-rich indoles with alkynes is also developed. This protocol provides a straightforward access to a variety of N-spiroheterocyclic molecules in excellent enantioselectivities (76 examples, up to 99% ee).

Cobalt-Catalyzed Cyclization of 2-Bromobenzamides with Carbodiimides: A New Route for the Synthesis of 3-(Imino)isoindolin-1-ones

A novel synthetic pathway to approach 3-(imino)isoindolin-1-ones by the Co-catalyzed cyclization reaction of 2-bromobenzamides with carbodiimides has been developed. This catalytic reaction can tolerate a variety of substituents and provide corresponding products in moderate yields for most cases. According to the literature, the reaction mechanism is proposed through the formation of a five-membered aza-cobalacycle complex, which carries out the following reaction subsequence, including nucleophilic addition and substitution, to furnish the desired structures.

Enantioselective synthesis of 1-aminoindene derivatives via asymmetric Brønsted acid catalysis

We describe a catalytic asymmetric iminium ion cyclization reaction of simple 2-alkenylbenzaldimines using a BINOL-derived chiral N-triflyl phosphoramide. The corresponding 1-aminoindenes and tetracyclic 1-aminoindanes are formed in good yields and high enantioselectivities. Further, the chemical utility of the obtained enantiopure 1-aminoindene is demonstrated for the asymmetric synthesis of (S)-rasagiline.

Further Developments and Applications of Oxazoline-Containing Ligands in Asymmetric Catalysis

The chiral oxazoline motif is present in many ligands that have been extensively applied in a series of important metal-catalyzed enantioselective reactions. This Review aims to provide a comprehensive overview of the most significant applications of oxazoline-containing ligands reported in the literature starting from 2009 until the end of 2018. The ligands are classified not by the reaction to which their metal complexes have been applied but by the nature of the denticity, chirality, and donor atoms involved. As a result, the continued development of ligand architectural design from mono(oxazolines), to bis(oxazolines), to tris(oxazolines) and tetra(oxazolines) and variations thereof can be more easily monitored by the reader. In addition, the key transition states of selected asymmetric transformations will be given to illustrate the features that give rise to high levels of asymmetric induction. As a further aid to the reader, we summarize the majority of schemes with representative examples that highlight the variation in % yields and % ees for carefully selected substrates. This Review should be of particular interest to the experts in the field but also serve as a useful starting point to new researchers in this area. It is hoped that this Review will stimulate both the development/design of new ligands and their applications in novel metal-catalyzed asymmetric transformations.

Highly Regio- and Enantioselective Reductive Coupling of Alkynes and Aldehydes via Photoredox Cobalt Dual Catalysis

A Co-catalyzed highly regio- and enantioselective reductive coupling of alkynes and aldehydes has been developed under visible light photoredox dual catalysis. A variety of enantioenriched allylic alcohols have been obtained by using unsymmetrical internal alkynes and commercially available catalyst, chiral ligand, and reagents. It is noteworthy that this approach has considerable advantages, such as excellent regio- (>95:5 for >40 examples), stereo- (up to >95:5 E/Z), and enantioselectivity (92-99% ee, >35 examples) control, mild reaction conditions, broad substrate scope, and good functional group compatibility, making it a great improvement to enantioselective alkyne-aldehyde reductive coupling reactions.

Transition-Metal-Catalyzed Addition/Cyclization Reactions of the C-N Multiple Bonds Containing Species

This article describes our research work for the past decade, which involves the transition-metal-catalyzed cyclization reactions of the C-N multiple bonds containing species and their synthetic applications to access various heterocyclic compounds. The concepts of reactions including four types of coupling with a subsequent cyclization are (1) the transition-metal performs as a Lewis acid to activate a nitrile and accelerate the nucleophilic addition, (2) the transition-metal-catalyzed 1,2-insertion reaction of nitrile, (3) the Cu-catalyzed C-N coupling reaction of imine, and (4) the Co-catalyzed addition/cyclization reaction of imine. These methods can be used to synthesize various N-containing aromatic heterocycles with higher efficiency, and can be applied to the synthesis of relevent natural alkaloids, their derivatives as well as biologically active compounds.

Cobalt-catalyzed coupling reactions of 2-halobenzamides with alkynes: investigation of ligand-controlled dual pathways

The Co-catalyzed reactions of 2-halobenzamides and alkynes to form quinolinones or 2-vinyl benzamides are described here. These two reactions can be controlled merely by ligands.

Copper-Catalyzed Dual Cyclization for the Synthesis of Quinindolines

A synthetic approach to quinindoline derivatives by the Cu-catalyzed dual cyclization has been developed. This catalytic reaction is a practical method for the systematic synthesis of quinindoline core structure, which contains a limited-step synthetic strategy and can tolerant a wide variety of substituents. In addition, the mechanistic study reveals that the reaction initiates from a Lewis acid accelerated addition of aniline to nitrile and provides the indole substructure, and then the subsequent Cu-catalyzed C-N coupling reaction furnishes the quinoline subunit and affords the quinindoline structure.

Transition-Metal-Free Tandem Cyclization/N-Arylation Reaction: A Method To Access Biaryl Sultam Derivatives via a Diradical Pathway

A novel procedure for the transition-metal-free tandem cyclization/N-arylation reaction sequence of an aryne with a 1,2,3,4-benzothiatriazine-1,1-dioxide is reported. This reaction goes through the intramolecular homolytic cyclization to generate an N-H biaryl sultam intermediate, which enables aryne insertion to access diversely functionalized biaryl sultam derivatives with high yields. The mechanism study indicates that homolytic cyclization is executed by a diradical species, initiated from the thermal decomposition of 1,2,3,4-benzothiatriazine-1,1-dioxide to release a nitrogen molecule.

Copper-catalyzed tandem cis-carbometallation/cyclization of imine-ynamides with arylboronic acids

An efficient copper-catalyzed tandem regioselective cis-carbometallation/cyclization of imine-ynamides with arylboronic acids has been developed. This method leads to a facile and practical synthesis of valuable 2,3-disubstituted indolines in moderate to excellent yields and features a broad substrate scope and wide functional group tolerance. Other significant features of this protocol include the use of readily available starting materials, high flexibility, simple procedure and mild reaction conditions.