Synthesis of Benzyl Amines via Copper-Catalyzed Enantioselective Aza-Friedel-Crafts Addition of Phenols to N-Sulfonyl Aldimines

Cu(II)-Catalyzed Enantioselective Aza-Friedel-Crafts Reaction of 1-Naphthols and Electron-Rich Phenols with Isatin-Derived Ketimines

New chiral ligands could be obtained by introducing proline moieties and imidazoline moieties to binaphthyl skeletons. The chiral ligands exhibited balanced rigidity and flexibility which could allow the change of the conformations during the reactions on one hand, and could provide sufficient asymmetric induction on the other. The proline moiety could act as a linker connecting the binaphthyl skeletons and the imidazoline moieties as well as a coordinating group for the central metal, and the electronic and steric properties of the imidazoline groups could be carefully fine-tuned by the use of different substituents. In the presence of Cu(II) catalyst bearing such chiral ligands, aza-Friedel-Crafts reaction of 1-naphthols and electron-rich phenols with isatin-derived ketimines provided the desired products with good to excellent yields and up to 99 % ee. The reactions showed good scalability, and excellent ee could still be obtained when the reaction was carried out in gram-scale.

Enantioselective Synthesis of Diarylmethylamines through the Aza-Friedel-Crafts Reaction of 1,3,5-Trialkoxy Benzenes and N-Sulfonyl Aldimines Catalyzed by BINOL-Derived Disulfonimides

A 1,1'-bi-2-naphthol (BINOL)-derived disulfonimide (DSI)-catalyzed enantioselective aza-Friedel-Crafts reaction between 1,3,5-trialkoxy benzenes and N-sulfonyl aldimines gives direct access to a series of chiral diarylmethylamines in good yields and good to excellent enantioselectivities (up to 97% ee). This reaction provides a useful protocol for the direct synthesis of diarylmethylamine derivatives.

Cu-Catalyzed Synthesis of Benzoxazole with Phenol and Cyclic Oxime

A Cu-catalyzed straightforward synthesis of benzoxazoles from free phenols and cyclic oxime esters is reported. The mild reaction conditions tolerate various electron-withdrawing and electron-donating functional groups on both substrates, affording benzoxazoles in moderate to good yields. With this protocol, large-scale syntheses of Ezutromid and Flunoxaprofe in one or two steps are demonstrated. A catalytic mechanism, which includes Cu-catalyzed amination via inner-sphere electron transfer and consequent annulation, is proposed.

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.

Straightforward Access to Anthrone Functionalized Benzylic Amines via Organocatalytic 1,2-Addition of Anthrones to Imines at Ambient Temperature

Activation of anthrone via benzylic deprotonation in the presence of triethylamine paves the way for the 1,2-addition reaction with imines to provide the desired functionalized anthrones in good to excellent yields under mild and operationally simple reaction conditions with a broad range of substrate scopes without using any external additives or toxic stoichiometric reagents.

Synthesis of Benzylureas and Related Amine Derivatives via Copper-Catalyzed Three-Component Carboamination of Styrenes

A direct assembly of secondary benzylureas and related amine derivatives via copper-catalyzed carboamination of styrenes with potassium alkyltrifluoroborates and ureas, anilines, or an amide is reported. Terminal and 1,2-disubstituted alkenes, as well as dienes, participate in this three-component coupling reaction. The reaction mechanism likely involves the addition of an alkyl radical to the styrene, followed by metal-mediated oxidative coupling of the resulting benzylic radical with the amine derivative. Factors that impact substrate reactivity and regioselectivity are discussed.

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.

Ruthenium-Catalyzed Hydrogen Evolution o-Aminoalkylation of Phenols with Cyclic Amines

Herein, we present a ruthenium-catalyzed new hydrogen evolution ortho-aminoalkylation of phenolic derivatives with cyclic amines as the coupling agents. The developed cross-coupling reaction offers a practical platform for direct access to a variety of functionalized phenols with the features of good substrate and functional group compatibility, readily available catalyst system and feedstocks, no need for additional sacrificial oxidants, and high atom efficiency.

Sulfur-Mediated Allylic C-H Arylation, Epoxidation, and Aziridination

Transition-metal-free, sulfur-mediated allylic C-H arylation, epoxidation, and aziridination were realized through one-pot procedures. The reaction design involved initial addition between olefins and triflic anhydride activated sulfoxides, followed by subsequent reactions of the allylic sulfur ylides generated under basic conditions with arylboronic acids, aldehydes, or aldimines, to give allylic arylation, epoxidation, or aziridination products, respectively.

Facile synthesis of chiral ε-sultams via an organocatalytic aza-Friedel-Crafts reaction

Chiral ε-sultams, with their unique strain cyclic structure, are a type of molecule with important biological activities. A facile enantioselective aza-Friedel-Crafts reaction of seven-membered cyclic N-sulfonylimines with naphthols was developed with a cinchona alkaloid-based bifunctional organocatalyst, giving chiral ε-sultams with an enantiomeric excess of up to 92%.

Delayed catalyst function enables direct enantioselective conversion of nitriles to NH2-amines

Accessing enantiomerically enriched amines often demands oxidation-state adjustments, protection and deprotection processes, and purification procedures that increase cost and waste, limiting applicability. When diastereomers can be formed, one isomer is attainable. Here, we show that nitriles, largely viewed as insufficiently reactive, can be transformed directly to multifunctional unprotected homoallylic amines by enantioselective addition of a carbon-based nucleophile and diastereodivergent reduction of the resulting ketimine. Successful implementation requires that competing copper-based catalysts be present simultaneously and that the slower-forming and less reactive one engages first. This challenge was addressed by incorporation of a nonproductive side cycle, fueled selectively by inexpensive additives, to delay the function of the more active catalyst. The utility of this approach is highlighted by its application to the efficient preparation of the anticancer agent (+)-tangutorine.

A Revised Modular Approach to (-)-trans-Δ8-THC and Derivatives Through Late-Stage Suzuki-Miyaura Cross-Coupling Reactions

A revised modular approach to various synthetic (–)‐trans‐Δ⁸‐THC derivatives through late‐stage Suzuki–Miyaura cross‐coupling reactions is disclosed. Ten derivatives were synthesized allowing both sp²‐ and sp³‐hybridized cross‐coupling partners with minimal β‐hydride elimination. Importantly, we demonstrate that a para‐bromo‐substituted THC scaffold for Suzuki–Miyaura cross‐coupling reactions has been initially reported incorrectly in recent literature.

A Novel Sc(OTf)3 -Catalyzed (2+2+1)-Cycloannulation/Aza-Friedel-Crafts Alkylation Sequence toward Multicyclic 2-Pyrrolines

The rapid assembly of molecular complexity continues to be at the forefront of novel reaction development. In the pursuit of that goal, we herein report a novel Sc(OTf)₃ -catalyzed, one-pot multicomponent reaction that furnishes complex multicyclic 2-pyrrolines with excellent overall yields and perfect diastereocontrol. This process is based on our previously established (2+2+1)-cycloannulation of in situ generated 1-azaallyl cations, 1,3-dicarbonyls and primary amines. The newly formed and highly reactive aminal moiety is readily substituted with indoles and pyrroles both as external and internal π-nucleophiles to provide densely functionalized N-heterocycles with four new σ-bonds and two vicinal quaternary stereogenic centers. In addition, DFT calculations have been conducted to further characterize the intermediate 1-azaallyl cations.