Chiral Binaphthol-Catalyzed Enantioselective Conjugate Addition of Alkenyl and Arylboronic Acids to α,β-Unsaturated Cyclic N-Sulfonyl Ketimines

The chiral binaphthol-catalyzed enantioselective conjugate addition of alkenylboronic acids and heteroarylboronic acids to cyclic N-sulfonyl ketimines is reported, providing the 1,4-addition products in high yields and moderate to excellent enantioselectivities (up to >99% ee). This mild, scalable catalytic system exhibits high efficiency and broad substrate scopes. Additionally, arylboronic acids were viable nucleophiles under more forcing conditions.

Strategies for the Development of Asymmetric and Non-Directed Petasis Reactions

The Petasis reaction is a multicomponent reaction of aldehydes, amines and organoboron reagents and is a useful method for the construction of substituted amines. Despite the significant advancement of the Petasis reaction since its invention in 1993, strategies for asymmetric and non-directed Petasis reactions remain limited. To date, there are very few catalytic asymmetric Petasis reactions and almost all asymmetric reports employ a chiral auxiliary. Likewise, the aldehyde component often requires a directing group, ultimately limiting the reaction's scope. In this Concept, key methods for asymmetric and non-directed Petasis reactions are discussed, focusing on how these conceptual advances can be applied to solve long-standing gaps in the Petasis literature.

Regio- and enantioselective nickel-alkyl catalyzed hydroalkylation of alkynes

The migratory insertion of metal-hydride into alkene has allowed regioselective access to organometallics, readily participating in subsequent functionalization as one conventional pathway of hydroalkylation, whereas analogous process with feedstock alkyne is drastically less explored. Among few examples, the regioselectivity of metal-hydride insertion is mostly governed by electronic bias of alkynes. To alter the regioselectivity and drastically expand the intermediate pools that we can access, one aspirational design is through alternative nickel-alkyl insertion, providing opposite regioselectivity induced by steric demand. Leveraging in situ formed nickel-alkyl species, we herein report the regio- and enantioselective hydroalkylation of alkynes with broad functional group tolerance, excellent regio- and enantioselectivity, enabling efficient route to diverse valuable chiral allylic amines motifs. Preliminary mechanistic studies indicate the aminoalkyl radical species can participate in metal-capture and lead to formation of nickel-alkyl, of which the migratory insertion is key to reverse regioselectivity observed in metal-hydride insertion.

Base mediated aza-[2 + 1] annulation and regioselective aziridine ring-opening cascade: mild synthesis of functionalized β-amino ketones from cyclic N-sulfonyl aldimines and α-carbonyl sulfonium salts

Cyclic N-sulfonyl aldimines are well-known aza-[2C]-synthons for various [2 + n] annulation reactions. Herein we describe a novel base mediated [2 + 1] annulation and a regioselective aziridine ring-opening reaction cascade, which provides an efficient and distinct synthetic strategy from readily available cyclic N-sulfonyl aldimines and α-carbonyl sulfonium salts leading to β-amino ketone derivatives through the corresponding fused tri-substituted aziridines. This one-pot, two-step process involves formation of C-C and C-N bonds and subsequent cleavage of a C-N bond. The features of the developed reaction include the use of mild reaction conditions, broad substrate scope, and excellent yields. The synthetic utility of this approach was demonstrated by gram-scale operation and further product derivatizations.

Nickel-Catalyzed Enantioselective Reductive Arylation and Heteroarylation of Aldimines via an Elementary 1,4-Addition

Nickel catalysts of chiral pyrox ligands promoted enantioselective reductive arylation and heteroarylation of aldimines, using directly (hetero)aryl halides and sulfonates. The catalytic arylation can also be conducted with crude aldimines generated from condensation of aldehydes and azaaryl amines. Mechanistically, density functional theory (DFT) calculations and experiments pointed to an elementary step of 1,4-addition of aryl nickel(I) complexes to N-azaaryl aldimines.

Rh(I)-Catalyzed Enantioselective Arylation of Cyclic N-Sulfonyl Diketimines Using Planar-Chiral Phosphine-Olefin Ligands Based on a (Cyclopentadienyl)manganese(I) Scaffold with a Highly Fluorinated Aryl Phosphino Group

Catalytic enantioselective 1,2-addition reactions of arylboronic acids with 1,2,5-thiadiazoline 1,1-dioxide derivatives were achieved using planar-chiral phosphine-olefin ligand L5 with a bis[(2,3,4,5,6-pentafluoro)phenyl]phosphino group, showing ≤98% ee. The enantioselectivities of the addition products were improved by increasing the number of fluoro substituents on the aromatic ring of the ligand. X-ray crystallographic studies of 3aa and [RhCl/L5]₂ revealed the absolute configuration of the enantioenriched addition product 3 and the mode of phosphine-olefin bidentate coordination of L5 to a rhodium(I) cation.

Construction of a MOF-Supported Palladium Catalyst via Metal Metathesis

A new MOF-supported heterogeneous palladium catalyst Pd/NBB-1 has been synthesized successfully through the effective metal metathesis between Pd(CF₃ COO)₂ and NBB-1. NBB-1 is a two-dimensional zinc metal-organic framework constructed from 2-aminoterephthalate (NH₂ -H₂ BDC) and 2,2'-bipyridine-5-carboxylate (HBPC) by solvothermal method. The replacement efficiency of Pd(II) to Zn(II) is up to 72% after only 24 hours, which is beneficial to the catalytic application. Pd/NBB-1 with a low loading of 2 mol% works efficiently in the 1,4-addition reaction of arylboronic acids with α,β-unsaturated ketones in air, and its catalytic activity keeps unchanged after 3 reaction cycles. This work provides a new strategy to effectively prepare supported noble metal/MOF catalysts, which would further increase the practical applications of metal-organic frameworks.

Chiral Diene Ligands in Asymmetric Catalysis

Asymmetric catalysis has emerged as a general and powerful approach for constructing chiral compounds in an enantioselective manner. Hence, developing novel chiral ligands and catalysts that can effectively induce asymmetry in reactions is crucial in modern chemical synthesis. Among such chiral ligands and catalysts, chiral dienes and their metal complexes have received increased attention, and a great progress has been made over the past two decades. This review provides comprehensive and critical information on the essential aspects of chiral diene ligands and their importance in asymmetric catalysis. The literature covered ranges from August 2003 (when the first effective chiral diene ligand for asymmetric catalysis was reported) to October 2021. This review is divided into two parts. In the first part, the chiral diene ligands are categorized according to their structures, and their preparation methods are summarized. In the second part, their applications in asymmetric transformations are presented according to the reaction types.

Natural Product-Inspired Chiral Ligand Design: Aloperine and N-Substituted Aloperines-Induced Pd-Catalyzed Asymmetric Hydroarylation of Ketimines

A naturally occurring alkaloid aloperine was utilized as a chiral skeleton for the development of new ligands/catalysts in asymmetric synthesis. A number of N-substituted aloperines have been prepared, and a Pd-catalyzed asymmetric hydroarylation of ketimines using these chiral 1,3-diamine ligands was reported. A range of chiral sulfonyl amides were prepared in high yields and enantioselectivities. The stereoselectivity and structure relationships of aloperines have been studied. In addition, preliminary studies on the desymmetrization of meso-anhydride have also shown that these diamines have good potential in organocatalysis. These discoveries would provide a new future development for natural product-inspired chiral ligand design and developments.

Synthesis of chiral branched allylamines through dual photoredox/nickel catalysis

Allylamines are versatile building blocks in the synthesis of various naturally occurring products and pharmaceuticals. In contrast to terminal allylamines, the methods of synthesis of their branched congeners with internal, stereodefined double bonds are less explored. This work describes a new approach for the preparation of allylamines via cross-coupling of alkyl bromides with simple 3-bromoallylamines by merging the photoredox approach and Ni catalysis. The reaction proceeds under mild conditions, under blue light irradiation, and in the presence of an organic dye, 4CzIPN, as a photocatalyst. The scope of suitable reaction partners is broad, including alkyl bromides bearing reactive functionalities (e.g., esters, nitriles, aldehydes, ketones, epoxides) and N-protected allylamines, as well as N-allylated secondary and tertiary amines and heterocycles. The employment of non-racemic starting materials allows for rapid and easy construction of complex multifunctional allylamine derivatives without the loss of enantiomeric purity.

Application of Rh(I)/Bicyclo[2.2.1]heptadiene Catalysts to the Enantioselective Synthesis of Chiral Amines

The development of efficient synthetic methods for accessing enantioenriched α-chiral amines is of great importance in the disciplines of medicinal and synthetic organic chemistry. Enantioselective Rh-catalyzed 1,2-addition reactions to activated imine derivatives are regarded as useful protocols for forming α-chiral amines. This personal account outlines our efforts to develop chiral bicyclo[2.2.1]heptadiene ligands for Rh-catalyzed asymmetric additions of various organoboron reagents to a wide range of imine derivatives. Transformations of the thus-obtained adducts into known natural products or molecules of pharmaceutical importance serve to confirm their synthetic usefulness.

Ag-Catalyzed ring-opening of tertiary cycloalkanols for C-H functionalization of cyclic aldimines

We firstly describe a silver-catalyzed direct C-H functionalization of cyclic aldimines with cyclopropanols and cyclobutanols via a radical-mediated C-C bond cleavage strategy. The desired products were generated in decent yields with wide substrate scope under mild reaction conditions. In addition, a gram-scale reaction and synthetic transformation of the product were performed.

Enantioselective Rhodium-Catalyzed Allylation of Aliphatic Imines: Synthesis of Chiral C-Aliphatic Homoallylic Amines

Reported herein is a method for the efficient syntheses of optically active 1-alkyl homoallylic amines in yields up to 95%, 13.5:1 dr, and 98% ee under mild, aqueous reaction conditions, via the Rh-catalyzed asymmetric allylation of aliphatic aldimines. This method provides a streamlined synthetic platform for the preparation of indolizidine and piperidine alkaloids, thus demonstrating its usefulness.

Nickel-Catalyzed Asymmetric Hydrogenation of Cyclic Sulfamidate Imines: Efficient Synthesis of Chiral Cyclic Sulfamidates

Chiral cyclic sulfamidates are useful building blocks to construct compounds, such as chiral amines, with important applications. Often these compounds can only be generated through expensive precious metal catalysts. Here, Ni(OAc)2/(S, S)-Ph-BPE-catalyzed highly efficient asymmetric hydrogenation of cyclic sulfamidate imines was successfully developed, affording various chiral cyclic sulfamidates with high yields and excellent enantioselectivities (up to 99% yield, >99% enantiomeric excess [ee]). This Ni-catalyzed asymmetric hydrogenation on a gram scale has been achieved with only 0.1 mol% catalyst loading in 99% yield with 93% ee. Other types of N-sulfonyl ketimines were also hydrogenated well to obtain the corresponding products with >99% conversion, 96%-97% yields, and 97%->99% ee. In addition, this asymmetric methodology could produce other enantioenriched organic molecules, such as chiral β-fluoroamine, amino ether, and phenylglycinol. Moreover, a reasonable catalytic cycle was provided according to the deuterium-labeling studies, which could reveal a possible mechanism for this Ni-catalyzed asymmetric hydrogenation.

Copper-Catalyzed Asymmetric Arylation of N-Heteroaryl Aldimines: Elementary Step of a 1,4-Insertion

Copper complexes of monodentate phosphoramidites efficiently promote asymmetric arylation of N-azaaryl aldimines with arylboroxines. DFT calculations and experiments support an elementary step of 1,4-insertion in the reaction pathway, a step in which an aryl-copper species adds directly across four atoms of C=N-C=N in the N-azaaryl aldimines.

Synthesis of chiral seven-membered cyclic sulfonamides through palladium-catalyzed arylation of cyclic imines

An enantioselective palladium-catalyzed addition of arylboronic acids to seven-membered cyclic N-sulfonyl aldimines and ketimines has been developed, giving the chiral cyclic sulfonamides with excellent yields and up to 99% ee.

Chemoselective cyclization of N-sulfonyl ketimines with ethenesulfonyl fluorides: access to trans-cyclopropanes and fused-dihydropyrroles

A stereo- and chemoselective ring closing reaction of N-sulfonyl ketimines with ethene sulfonyl fluorides promoted by DBU is reported. This selective C–C vs. C–N bond cyclization process delivers to trans-cyclopropanes (dr up to ≤99 : 1) and fused-dihydropyrroles.

Rhodium-Catalyzed Asymmetric Addition of Organoboronic Acids to Aldimines Using Chiral Spiro Monophosphite-Olefin Ligands: Method Development and Mechanistic Studies

The synthesis of a novel type of chiral spiro monophosphite-olefin (SMPO) ligands based on a hexamethyl-1,1'-spirobiindane scaffold was accomplished starting from Bisphenol C. The optimal ligand could serve as an elegant chiral bidentate ligand in the Rh-catalyzed asymmetric 1,2-addition of organoboronic acids to various acyclic/cyclic aldimines, leading to chiral amines with high yields and excellent enantioselectivities. Detailed stereochemical models for enantioselective induction were elucidated through DFT calculations and postulated the origins of the higher enantioselectivity of phosphite-olefin ligands.

Metal- and base-free synthesis of functionalized α,α-difluoroimines via electrophilic fluorination of N-substituted enamines

A metal- and base-free synthesis of functionalized α,α-difluoroimines is presented. The reaction features mild conditions, high E/Z control and broad functional group tolerance. The utility of the products was demonstrated through valuable synthetic transformations.

Ni(II)-catalyzed asymmetric alkenylations of ketimines

Chiral allylic amines are not only present in many bioactive compounds, but can also be readily transformed to other chiral amines. Therefore, the asymmetric synthesis of chiral allylic amines is highly desired. Herein, we report two types of Ni(II)-catalyzed asymmetric alkenylation of cyclic ketimines for the preparation of chiral allylic amines. When ketimines bear alkyl or alkoxycarbonyl groups, the alkenylation gives five- and six-membered cyclic α-tertiary allylic amine products with excellent yields and enantioselectivities under mild reaction conditions. A variety of ketimines can be used and the method tolerates some variation in alkenylboronic acid scope. Furthermore, with alkenyl five-membered ketimine substrates, an alkenylation/rearrangement reaction occurs, providing seven-membered chiral sulfamide products bearing a conjugated diene skeleton with excellent yields and enantioselectivities. Mechanistic studies reveal that the ring expansion step is a stereospecific site-selective process, which can be catalyzed by acid (Lewis acid or Brønsted acid).

Chiral allylic amines are often encountered in bioactive compounds and can be conveniently transformed into other chiral amines. Here, the authors report nickel-catalyzed enantioselective addition and addition/ring-expansion of alkenylboronic acids to ketimines providing a range of valuable chiral azaheterocycles.

Rhodium-Catalyzed Enantioselective Alkenylation of Cyclic Ketimines: Synthesis of Multifunctional Chiral α,α-Disubstituted Allylic Amine Derivatives

By employing a simple open-chain chiral phosphite-olefin ligand, a highly enantioselective rhodium-catalyzed alkenylation of 1,2,5-thiadiazole 1,1-dioxide-type cyclic ketimines with diverse vinylboronic acids was achieved under mild conditions at room temperature. This protocol provides an efficient and practical access to multifunctional α,α-disubstituted chiral allylic amines bearing quaternary stereocenters in high yields (up to 99%) with good to excellent ee's (up to 99%).

Recent advances in rhodium-catalyzed asymmetric synthesis of heterocycles

Heterocycles are crucial structural motifs that are ubiquitously present in biologically active natural products and pharmaceutically important compounds. Over the past few decades, great attention has been paid to develop efficient methodologies for the construction of diverse enantioenriched heterocyclic frameworks. This review focuses on the recent impressive progress and advances in the asymmetric synthesis of heterocycles under rhodium catalysis.

Cyclic imines – preparation and application in synthesis

Cyclic imines, available from various nitrogen-containing reactants, serve as versatile synthetic intermediates for biologically active compounds.

Pd(ii), Ni(ii) and Co(ii)-catalyzed enantioselective additions of organoboron reagents to ketimines

This feature article highlights the development of Pd(ii), Ni(ii), and Co(ii)-catalyzed asymmetric additions of organoboron reagents to ketimines.

Rh-Catalyzed Enantioselective Allylation of N-Tosyl- and N-Nosylaldimines: Total Synthesis of (-)-Crispine A

The unprecedented development of asymmetric Rh-catalyzed 1,2-allylation of N-Ts- and N-Ns-aldimines is achieved. This protocol utilizes potassium allyltrifluoroborates and various aldimines to generate enantioenriched homoallylic amines in the presence of 3.0 mol % of Rh(I)/L1b catalyst with up to 90% yield, 98% ee (R = H), and 10:1 diastereoselectivity (R = Me or Ph), yielding the same major diastereomer when using potassium (E)- and (Z)-crotyltrifluoroborate. Its synthetic utility is also illustrated in the total synthesis of (-)-crispine A.

Enantioselective Rhodium-Catalyzed Coupling of Arylboronic Acids, 1,3-Enynes, and Imines by Alkenyl-to-Allyl 1,4-Rhodium(I) Migration

A chiral rhodium complex catalyzes the highly enantioselective coupling of arylboronic acids, 1,3-enynes, and imines to give homoallylic sulfamates. The key step is the generation of allylrhodium(I) species by alkenyl-to-allyl 1,4-rhodium(I) migration.