Enantioselective Aza-Morita-Baylis-Hillman Reactions of Acrylonitrile Catalyzed by Palladium(II) Pincer Complexes havingC2-Symmetric Chiral Bis(imidazoline) Ligands

Synthesis of CF3-Containing 2-Imidazolines and Imidazoles via a Iodide-Promoted [3 + 2] Cyclization Reaction

We report herein a general and effective system achieving cyclization of β-trifluoromethyl enones with amidines in the presence of 1,3-diiodo-5,5-dimethylhydantoin (DIH), which affords a range of trifluoromethylated 2-imidazolines in synthetically useful yields with good diastereoselectivities (up to 95% yield, up to 98:2 dr) and good functional group tolerance. Furthermore, the one-pot synthesis of trifluoromethylated imidazoles via sequential cyclization and oxidation is demonstrated. More significantly, the reaction mechanism was verified by ESI-MS studies of possible intermediates, and a reasonable reaction mechanism was proposed.

Iridium-Catalyzed Enantioselective Formal α-Allylic Alkylation of Acrylonitrile

A highly enantioselective formal α-allylic alkylation of acrylonitrile is developed using 4-cyano-3-oxotetrahydrothiophene (c-THT) as a safe and easy-to-handle surrogate of acrylonitrile. This two-step process consists of an Ir(I)/(P,olefin)-catalyzed branched-selective allylic alkylation using easily accessible branched rac-allylic alcohols as the allylic electrophile followed by retro-Dieckmann/retro-Michael fragmentation and is shown to be applicable for the enantioselective synthesis of α-allylic acrylates as well as α-allylic acrolein.

Enantioselective reaction of N-cyano imines: decarboxylative Mannich-type reaction with malonic acid half thioesters

The enantioselective reaction of imines bearing a cyano group as an activating group with malonic acid half thioesters gave chiral cyanamide derivatives with high enantioselectivity. The density functional theory (DFT) calculation clarified the stereochemical outcome and importance of the N-cyano group for imines.

Chiral (phosphine)-(imidazoline) PCN pincer palladium(II) complexes: synthesis and application in asymmetric hydrophosphination of 2-alkenoylpyridines with diphenylphosphine

A series of new chiral PCN pincer Pd(II) complexes 3a−l with aryl-based (phosphine)-(imidazoline) ligands were conveniently synthesized from readily available starting materials with the key step being phosphination/C−H palladation reaction....

Cu-catalyzed cyanomethylation of imines and α,β-alkenes with acetonitrile and its derivatives

We describe copper-catalyzed cyanomethylation of imines and α,β-alkenes with a methylnitrile source and provide an efficient route to synthesize arylacrylonitriles and β,γ-unsaturated nitriles. This method tolerates aliphatic and aromatic alkenes substituted with a variety of functional groups such as F, Cl, Br, Me, OMe, tert-Bu, NO2, NH2 and CO2H with good to excellent yields (69-98%). These systems consist of inexpensive, simple copper catalyst and acetonitrile with its derivatives (α-bromo/α-iodo-acetonitrile) and are highly applicable in the industrial production of acrylonitriles.

Electrochemical tandem trifluoromethylation of allylamines/formal (3 + 2)-cycloaddition for the rapid access to CF3-containing imidazolines and oxazolidines

A straightforward and environmentally friendly synthesis of CF₃-containing imidazolines and oxazolidines has been developed through an electrochemical three-component reaction among allylamines, the Langlois reagent, and nitrile or carbonyl compounds.

Direct Access to Highly Enantioenriched α-Branched Acrylonitriles through a One-Pot Sequential Asymmetric Michael Addition/Retro-Dieckmann/Retro-Michael Fragmentation Cascade

A highly enantioselective synthesis of α-branched acrylonitriles is reported featuring a one-pot sequential asymmetric Michael addition/retro-Dieckmann/retro-Michael fragmentation cascade. The method, which relies on a solid, bench-stable, and commercially available acrylonitrile surrogate, is practical, scalable, and highly versatile and provides a direct access to a wide range of enantioenriched nitrile-containing building blocks. Most importantly, the method offers a new tool to incorporate an acrylonitrile moiety in an asymmetric fashion.

Planar chiral palladacycle precatalysts for asymmetric synthesis

Chiral non-racemic palladacycles were employed as precatalysts for Pd(0) mediated asymmetric synthesis. Addition of HPAr2/base to a ferrocenyloxazoline planar chiral palladacycle resulted in ligand synthesis and palladium capture to give a bidentate Phosferrox/Pd(0) complex. A series of these complexes were generated in situ and applied successfully as catalysts for asymmetric allylic alkylation.

1-Benzyl-2-(thien-2-yl)-4,5-dihydro-1H-imidazole

Imidazolines are a valuable class of organic compounds, namely ligands of imidazoline receptors, chiral ligands for metal catalysis, synthetic intermediates. The title compound has been prepared through a modified procedure, employing N-benzylethylenediamine and thiophene-2-carbaldehyde under the action of N-bromosuccinimide (NBS) in dichloromethane (DCM) in a good 78% yield.

Organocatalytic Synthesis of Highly Functionalized Heterocycles by Enantioselective aza-Morita-Baylis-Hillman-Type Domino Reactions

Organocatalytic enantioselective domino reactions are an extremely attractive methodology, as their use enables the construction of complex chiral skeletons from readily available starting materials in two or more steps by a single operation under mild reaction conditions. Thus, these reactions can save both the quantity of chemicals and length of time typically required for the isolation and/or purification of synthetic intermediates. Additionally, no metal contamination of the products occurs, given that organocatalysts include no expensive or toxic metals. The aza-Morita-Baylis-Hillman (aza-MBH) reaction is an atom-economical carbon-carbon bond-forming reaction between α,β-unsaturated carbonyl compounds and imines mediated by Lewis base (LB) catalysts, such as nucleophilic phosphines and amines. aza-MBH products are functionalized chiral β-amino acid derivatives that are highly valuable as pharmaceutical raw materials. Although various enantioselective aza-MBH processes have been investigated, very few studies of aza-MBH-type domino reactions have been reported due to the complexity of the aza-MBH process, which involves a Michael/Mannich/H-transfer/β-elimination sequence. Accordingly, in this review article, our recent efforts in the development of enantioselective domino reactions initiated by MBH processes are described. In the domino reactions, chiral organocatalysts bearing Brønsted acid (BA) and/or LB units impart synergistic activation to substrates, leading to the easy synthesis of highly functionalized heterocycles (some of which have tetrasubstituted and/or quaternary carbon stereocenters) in high yield and enantioselectivity.

Synthesis of Diastereoenriched α-Aminomethyl Enaminones via a Brønsted Acid-Catalyzed Asymmetric aza-Baylis-Hillman Reaction of Chiral N-Phosphonyl Imines

An effective chiral GAP methodology for preparing α-aminomethyl enaminones through a (R)-CSA-catalyzed asymmetric aza-Baylis-Hillman reaction is reported. Excellent yields and high diastereoselectivity could be obtained under mild conditions and convenient GAP techniques. The confirmations of the absolute configuration of N-phosphonyl imine and chiral enaminone by X-ray diffraction provides an explicit explanation of the chirality mechanism for GAP chemistry.

One-Pot Synthesis of Aza-Morita-Baylis-Hillman Adducts via Zinc-Mediated Allylation of 4-Bromocrotonates and Imines

An approach to the synthetically valuable β-substituted aza-Morita-Baylis-Hillman (MBH) type products, through zinc-mediated allylation of imines with 4-bromocrotonates followed by subsequent isomerization of the double bond, was developed. Complementary to classical MBH reaction, this reaction utilizes easily available 4-bromocrotonates as the reaction partners, providing a rapid alternative to the traditional use of α,β-unsaturated carbonyl compounds. The short reaction time, one-pot operation, broad substrate scopes, gram-scale synthesis, and synthetic application exemplified the utility and practicability of this method.

Chiral palladium pincer complexes for asymmetric catalytic reactions

Palladium pincer complexes, containing a monoanionic terdentate ligand composed of an anionic aryl carbon atom and two mutually compatible donor sites, have aroused considerable interest since their first reports in the late 1970s. The high stability of the Pd pincer complexes and particularly their high modularity make these species ideal candidates for catalysis. Furthermore, the nature of the meridional coordination of the pincer ligands, and along with this their ability to enforce a stereo-specific environment around the Pd center, provide a good opportunity for developing chiral Pd pincer catalysts. Thus, a broad variety of chiral Pd pincer complexes have been prepared by the introduction of various stereochemical centers in the pincer skeletons. These chiral Pd pincer complexes have been successfully applied to many asymmetric catalytic reactions such as hydrophosphination reactions, allylation of aldehydes and imines, Michael and aldol reactions, Suzuki-Miyaura reactions as well as reactions of nitrile compounds with imines. This review focuses on the synthetic methods and the applications of chiral Pd pincer complexes in asymmetric catalysis.

Enantioselective conjugate addition of an α,α-dithioacetonitrile with nitroalkenes using chiral bis(imidazoline)–Pd complexes

The first highly enantioselective reaction of α,α-dithioacetonitriles with nitroolefins as electron deficient olefins using chiral Phebim–Pd catalysts was developed.

Dinuclear PhosphoiminoBINOL-Pd Container for Malononitrile: Catalytic Asymmetric Double Mannich Reaction for Chiral 1,3-Diamine Synthesis

A phosphoiminoBINOL ligand was designed to form a dinuclear metal complex that could hold a malononitrile molecule. The dinuclear bis(phosphoimino)binaphthoxy-Pd₂(OAc)₂ complex catalyzed a double Mannich reaction of N-Boc-imines with malononitrile to give chiral 1,3-diamines with high enantioselectivity. The rational asymmetric catalyst, which smoothly introduces the first coupling product to the second coupling reaction while avoiding the reverse reaction, facilitates the over-reaction into a productive reaction process.

Enantioselective aza-Friedel–Crafts reaction of cyclic ketimines with indoles using chiral imidazoline–phosphoric acid catalysts

A highly enantioselective aza-Friedel Crafts reaction of cyclic 4-aryl-3-oxo-1,2,5-thiadiazol-1,1-oxides as cyclic ketimines with indoles was developed.

Enantioselective Barbier-type allylation of ketones using allyl halide and indium in water

We disclose herein an efficient enantioselective Barbier-type allylation of ketones using allyl halide and indium metal in water.

Direct catalytic enantioselective Mannich-type reaction of α,α-dithioacetonitriles with imines using chiral bis(imidazoline)–Pd complexes

The first highly enantioselective reaction of α,α-dithioacetonitriles with imines has been developed.

Desymmetrization of aziridine with malononitrile using cinchona alkaloid amide/zinc(ii) catalysts

The catalytic enantioselective desymmetrization of aziridines with malononitrile has been developed.

Iridium(iii)-bis(imidazolinyl)phenyl catalysts for enantioselective C-H functionalization with ethyl diazoacetate

The intermolecular enantioselective C-H functionalization with acceptor-only metallocarbenes is reported using a new family of Ir(iii)-bis(imidazolinyl)phenyl catalysts, developed based on the interplay of experimental and computational insights. The reaction is tolerant of a variety of diazoacetate precursors and is found to be heavily influenced by the steric and electronic properties of the substrate. Phthalan and dihydrofuran derivatives are functionalized in good yields and excellent enantioselectivities.

Dual Palladium(II)/Tertiary Amine Catalysis for Asymmetric Regioselective Rearrangements of Allylic Carbamates

The streamlined catalytic access to enantiopure allylic amines as valuable precursors towards chiral β- and γ-aminoalcohols as well as α- and β-aminoacids is desirable for industrial purposes. In this article an enantioselective method is described that transforms achiral allylic alcohols and N-tosylisocyanate in a single step into highly enantioenriched N-tosyl protected allylic amines via an allylic carbamate intermediate. The latter is likely to undergo a cyclisation-induced [3,3]-rearrangement catalysed by a planar chiral pentaphenylferrocene palladacycle in cooperation with a tertiary amine base. The otherwise often indispensable activation of palladacycle catalysts by a silver salt is not required in the present case and there is also no need for an inert gas atmosphere. To further improve the synthetic value, the rearrangement was used to form dimethylaminosulfonyl-protected allylic amines, which can be deprotected under non-reductive conditions.

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.

Aza-Morita–Baylis–Hillman reactions catalyzed by a cyclopropenylidene

Catalysis using a bis(dialkylamino)cyclopropenylidene (BAC) has been developed, which relies on a formal umpolung activation of Michael acceptor pro-nucleophiles.

Direct catalytic enantioselective Mannich-type reaction of dichloroacetonitrile using bis(imidazoline)-Pd catalysts

The catalytic enantioselective Mannich-type reaction of dichloroacetonitrile with imines has been developed.