Asymmetric Synthesis of α-Branched Allylic Amines by the Rh(I)-Catalyzed Addition of Alkenyltrifluoroborates to N-tert-Butanesulfinyl Aldimines

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.

Rhodium(III)-catalyzed three-component C(sp2)-H activation for the synthesis of amines

Rhodium-catalyzed three-component C-H bond activation of aromatics with amides and aldehydes to synthesize amines was established. The addition of copper was found to be essential to ensure the high reactivity. The mechanistic studies indicated that key intermediates formed by the transmetallization between rhodium and copper could further promote the addition between 2-(pyridin-2-yl)-phenyl-metal species and imines. A series of densely substituted amines could be conveniently prepared by this one-step, three-component procedure from commercially available substrates via C-H bond activation with water as the only by-product.

Enantioselective Synthesis of Chiral 2-Nitroallylic Amines via Cooperative Cation-Binding Catalysis

Chiral allylic amines are valuable building blocks for biologically important compounds and natural products. In this study, we present the use of cooperative cation-binding catalysis as an efficient method for synthesizing chiral allylic amines. By utilizing a chiral oligoEG and potassium fluoride as a cation-binding catalyst and base, respectively, a wide range of biologically relevant chiral 2-nitroallylic amines are obtained with excellent enantioselectivities (up to >99 % ee) through the organocatalytic asymmetric aza-Henry-like reaction of β-monosubstituted and β,β-disubstituted nitroalkenes with α-amidosulfones as imine precursors. Extensive experimental studies are presented to illustrate plausible mechanisms. Preliminary use of a chiral 2-nitroallylic amine as a Michael acceptor demonstrated its potential application for diversity-oriented synthesis of bioactive compounds.

Enantioselective Conjugate Addition of Alkenyl Trifluoroborates to Alkenyl-Substituted Benzimidazoles Catalyzed by Chiral Binaphthols

The enantioselective organocatalytic conjugate alkenylation of β-substituted alkenyl benzimidazoles afforded β-stereogenic 2-alkyl benzimidazole derivatives in excellent enantioselectivities. Chiral binaphthols were effective catalysts for promoting the nucleophilic addition of bench-stable alkenyl trifluoroborate salts under mild conditions, expanding their applications by utilizing C=N-containing azaarenes as activating groups. The synthetic utility of this strategy is demonstrated by conversions into several useful enantiomerically enriched benzimidazole building blocks.

Rh-Catalyzed diastereoselective addition of arylboronic acids to α-keto N-tert-butanesulfinyl aldimines: synthesis of α-amino ketones

Herein we present a diastereoselective addition of arylboronic acids to α-keto N-tert-butanesulfinyl aldimines catalyzed by a Rh(i) catalyst.

Direct Synthesis of Allyl Amines with 2-Nitrosulfonamide Derivatives via the Tsuji-Trost Reaction

The Tsuji-Trost Reaction is a palladium-catalysed allylation of nucleophiles that consists in the reaction of a nitrogen, carbon or oxygen-based nucleophiles with an allylic substrate bearing a leaving group. Here we present the use of 2-nitrosulfonamide derivatives as nucleophile, which are reactive under mild conditions. 2-nitrosulfonyl groups are well-known dual protective activator groups easy to introduce in any type of amine substrates. The resulting 2-nitrosulfonamide derivatives are ideal substrates for the Tsuji-Trost reaction to afford a convenient and flexible access to primary and dissymmetric secondary allyl amines. The optimised procedure is flexible (for solvent, temperature, functional groups) and has been applied with good to excellent yield to access to a wide range of allyl amine derivatives.

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.

TMSOTf-mediated synthesis of skipped dienes through the addition of olefins to imines and semicyclic N,O-acetals

A novel approach to skipped dienes has been developed through the TMSOTf-mediated one-pot addition-substitution of olefins 2a, 2f and 2g with imines 1a-1g, and a series of aryl substituted skipped dienes 3aa-3gf were accordingly obtained in 62%-94% yields. Moreover, semicyclic N,O-acetals 5 and 7 could also undergo this transformation to produce the corresponding skipped dienes 6aa and 6af-6al and 8ba and 8bf-8bk in moderate to good yields.

Intermolecular Hydroaminoalkylation of Alkynes

Intermolecular hydroaminoalkylation reactions of alkynes with secondary amines, which selectively give access to allylic amines with E configuration of the alkene unit, are achieved in the presence of titanium catalysts. Successful reactions of symmetrically substituted diaryl- and dialkylalkynes as well as a terminal alkyne take place with N-benzylanilines, N-alkylanilines, and N-alkylbenzylamines.

Allylic Amination of Alkenes with Iminothianthrenes to Afford Alkyl Allylamines

Allylic C-H amination is currently accomplished with (sulfon)amides or carbamates. Here we show the first allylic amination that can directly afford alkyl allylamines, enabled by the reactivity of thianthrene-based nitrogen sources that can be prepared from primary amines in a single step.

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.

Modern Stereoselective Synthesis of Chiral Sulfinyl Compounds

Chiral sulfinyl compounds, sulfoxides, sulfoximines, sulfinamides, and other derivatives, play an important role in asymmetric synthesis as versatile auxiliaries, ligands, and catalysts. They are also recognized as pharmacophores found in already marketed and well-sold drugs (e.g., esomeprazole) and used in drug design. This review is devoted to the modern methods of preparation of sulfinyl derivatives in enantiopure or enantiomerically enriched form. Selected new approaches leading to racemic products for which the asymmetric variant can be developed in the future are mentioned as well.

Nickel-Catalyzed Chemoselective Asymmetric Hydrogenation of α,β-Unsaturated Ketoimines: An Efficient Approach to Chiral Allylic Amines

An efficient synthetic route to chiral allylic amines has been developed by nickel/(S,S)-Ph-BPE complex catalyzed chemoselective asymmetric hydrogenation of α,β-unsaturated ketoimines. Varieties of α,β-unsaturated ketoimines have been well tolerated in this transformation to give chiral allylic amines with high yields and excellent ee values (up to 99% yield, up to 99% ee). A gram-scale reaction with 0.2 mol % catalyst loading has also been achieved.

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%).

Enantioselective synthesis of β-substituted chiral allylic amines via Rh-catalyzed asymmetric hydrogenation

Rh–DuanPhos complex-catalyzed asymmetric hydrogenation of α-alkenyl substituted enamides has been developed, which provides a readily accessible approach to chiral allylic amines with excellent enantioselectivities and high regioselectivities.

Titanium-mediated reductive cross-coupling reactions of imines with terminal alkynes: An efficient route for the synthesis of stereodefined allylic amines

Low-valency titanium species, generated in situ by using Ti(OiPr)₄/2 c-C₅H₉MgCl reagent, react with imines to give a titanium-imine complex that can couple with terminal alkynes to provide azatitanacyclopentenes with excellent regioselectivity. Stereodefined allylic amines are obtained in good yields after hydrolysis or iodonolysis of the corresponding azatitanacyclopentenes. When ethynylcyclopropane is used as the coupling partner to react with imines in this reaction, the initially generated allylic amine undergoes an unexpected 1,3-amino migration on silica gel during the column chromatography.

Chiral sulfur compounds studied by Raman optical activity: tert-butanesulfinamide and its precursor tert-butyl tert-butanethiosulfinate

Two chiral sulfur compounds, tert-butyl tert-butanethiosulfinate (1) and tert-butanesulfinamide (2), with inversion of configuration, have been studied by Raman optical activity (ROA) and electronic circular dichroism combined with density functional theory calculation. With the S-S linkage in 1, the couplings between the two tertiary carbon atoms often generate large ROA signals, whereas the tertiary carbon atom itself generally makes a large contribution to ROA signals in 2 for similar vibrational modes. The conformational dependence of ROA parameters provides probing conformation around the S-S bond from a new perspective. The simultaneous use of electronic circular dichroism and ROA is warranted to extract reliable conformational information. ROA provides a suitable candidate for the stereochemical study of chiral sulfur compounds, especially its capability of sensing the conformation around the S-S bond.

Enantioselective total synthesis of (+)-amabiline

The first total synthesis of (+)-amabiline, an unsaturated pyrrolizidine alkaloid from Cynoglossum amabile, is reported. This convergent, enantioselective synthesis proceeds in 15 steps (10-step longest linear sequence) in 6.2% overall yield and features novel methodology to construct the unsaturated pyrrolizidine or (-)-supinidine core.

Allylic Amines as Key Building Blocks in the Synthesis of (E)-Alkene Peptide Isosteres

Nucleophilic imine additions with vinyl organometallics have developed into efficient, high yielding, and robust methodologies to generate structurally diverse allylic amines. We have used the hydrozirconation-transmetalation-imine addition protocol in the synthesis of allylic amine intermediates for peptide bond isosteres, phosphatase inhibitors, and mitochondria-targeted peptide mimetics. The gramicidin S-derived XJB-5-131 and JP4-039 and their analogs have been prepared on up to 160 g scale for preclinical studies. These (E)-alkene peptide isosteres adopt type II' β-turn secondary structures and display impressive biological properties, including selective reactions with reactive oxygen species (ROS) and prevention of apoptosis.

Highly diastereoselective and general synthesis of primary β-fluoroamines

A short, high yielding protocol has been developed for the highly diastereoselective (dr >20:1) and general synthesis of primary β-fluoroamines by the enantioselective α-fluorination of aldehydes, conversion into the N-sulfinyl aldimine, nucleophilic addition of various organometallic species, and 1° amine liberation.