Highly enantioselective synthesis of chiral allenes by sequential creation of stereogenic center and chirality transfer in a single pot operation

Chiral allenes are readily accessed in a single pot operation in the reaction of terminal alkynes, aldehydes, chiral secondary amines, and zinc halides in good yields (up to 77% yield) and excellent enantioselectivities (up to 99% ee) in toluene at 120 °C. The reaction proceeds through initial formation of chiral propargylamine intermediates with creation of a new stereogenic center and subsequent chirality transfer via an intramolecular hydride shift to produce chiral allenes with high enantiomeric purities.     

Asymmetric Hydrophosphinylation of Alkynes: Facile Access to Axially Chiral Styrene-Phosphines

A Cu/CPA co-catalytic system has been developed for achieving the direct hydrophosphinylation of alkynes with phosphine oxides in delivering novel axially chiral phosphorus-containing alkenes in high yields and excellent enantioselectivities (up to 99 % yield and 99 % ee). DFT calculations were performed to elucidate the reaction pathway and the origin of enantiocontrol. This streamlined and modular methodology establishes a new platform for the design and application of new axially chiral styrene-phosphine ligands.     

Enantioselective Synthesis of C−N Axially Chiral N‐Aryloxindoles by Asymmetric Rhodium‐Catalyzed Dual C−H Activation

The first enantioselective Satoh–Miura‐type reaction is reported. A variety of C?N axially chiral N‐aryloxindoles have been enantioselectively synthesized by an asymmetric rhodium‐catalyzed dual C?H activation reaction of N‐aryloxindoles and alkynes. High yields and enantioselectivities were obtained (up to 99 % yield and up to 99 % ee). To date, it is also the first example of the asymmetric synthesis of C?N axially chiral compounds by such a C?H activation strategy.     

Synthesis of Chiral Diarylmethylamines by Cobalt-Catalyzed Enantioselective C-H Alkoxylation

Chiral diarylmethylamines (DAMA) are important structural motifs widely present in pharmaceuticals, natural products, and chiral ligands. Herein, we reported a highly enantioselective synthesis of chiral DAMAs via cobalt-catalyzed enantioselective C−H alkoxylation strategy. The reaction features easy operation, the use of earth-abundant and cost-efficient cobalt(II) catalyst, and readily available ligand. A range of chiral DAMAs were efficiently synthesized in high yields with excellent enantioselectivities (up to 90 % yield and up to 99 % ee) through desymmetrization and parallel kinetic resolution. Moreover, this protocol was also compatible with the synthesis of chiral benzylamines via kinetic resolution.     

Chiral Brønsted acid-catalyzed regio- and enantioselective arylation of α,β-unsaturated trifluoromethyl ketones

The interesting examples of chiral phosphoric acid-catalyzed regio- and enantioselective arylation of α,β-unsaturated trifluoromethyl ketones were reported. The reaction proceeded well and the desired products were obtained in good yields (up to 99%) with moderate to good enantioselectivities (up to 88% ee). Several desired products were obtained with excellent optical purities after a single recrystallization. Subsequent reduction of enantiopure products with NaBH₄ afforded two diastereomers of chiral trifluoromethyl-substituted secondary alcohols with high enantioselectivities (98% ee).     

Highly enantioselective Friedel-Crafts reaction of indoles with 2-enoylpyridine 1-oxides catalyzed by chiral pyridine 2,6-bis(5',5'-diphenyloxazoline)-Cu(II) complexes

The catalytic enantioselective Friedel-Crafts reaction of indoles with 2-enoylpyridine 1-oxides has been studied in the presence of chiral pyridine 2,6-bis(5',5'-diphenyloxazoline)-Cu(II) complexes. The reaction furnished alkylated indoles in excellent yields (up to 97%) and enantioselectivities (up to 99% ee).     

C1‐Symmetric Bicyclo[2.2.2]octa‐2,5‐diene (bod*) Ligands in Rhodium‐Catalyzed Asymmetric 1,4‐Addition of Arylboronic Acids to Enones and 1,2‐Addition to N‐[(4‐Nitrophenyl)sulfonyl]imines

A set of ten C₁‐symmetric chiral bicyclo[2.2.2]octa‐2,5‐dienes (bod*) 2 (Fig. 1) were tested as ligands in Rh‐catalyzed arylation reactions. The 1,4‐addition of arylboronic acids to cyclohex‐2‐en‐1‐one, cyclopent‐2‐en‐1‐one, and tert‐butyl cinnamate proceeded smoothly with excellent enantioselectivities (up to 99% ee; Tables 1–3). The challenging 1,2‐addition of triphenylboroxine to N‐[(4‐nitrophenyl)sulfonyl]imines yielded the product in high yield and in good enantioselectivity (up to 92% ee; Table 4). Generally, the use of C₁‐symmetric chiral bod* ligands bearing bulky substituents resulted in lower enantioselectivities, whereas several electron‐poor and electron‐rich bod* ligands gave higher enantioselectivities than the benchmark ligands reported in literature.     

An efficient organocatalytic method for highly enantioselective Michael addition of malonates to enones catalyzed by readily accessible primary amine-thiourea

A practical and highly enantioselective Michael addition of malonates to enones catalyzed by simple and readily available bifunctional primary amine-thiourea derived from 1,2-diaminocyclohexane is reported. The addition of weak acids and elevated temperature (ca. 50 °C) improved the efficiency of the Michael reaction. This approach enables the efficient synthesis of 1,5-ketoesters with good yields, excellent enantioselectivities (up to 99% ee), and low loading (0.5-5 mol %) of simple chiral primary amine-thiourea catalysts, and is applicable in multigram scale synthesis.     

Highly Efficient Asymmetric Synthesis of Enantiopure Dihydro-1,2-oxazines: Dual-Organocatalyst-Promoted Asymmetric Cascade Reaction

A one-pot dual-organocatalyst-promoted asymmetric α-aminoxylation/aza-Michael/aldol consendation cascade reaction is presented. The targeted optically active 1,2-oxazine derivatives are synthesized in moderate yields (up to 70%), excellent enantioselectivities (ee >99% in all cases), and excellent diastereoselectivities (dr up to >99:1) under mild conditions. To further elucidate the synthetic utility of the cascade products, cleavage of the N-O bond is demonstrated and an enantiopure syn-1,4-amino alcohol derivative is achieved in excellent yield.     

Efficient enantioselective additions of terminal alkynes and aldehydes under operationally convenient conditions

[reaction: see text] The enantioselective addition reaction of terminal acetylenes and aldehydes mediated by Zn(OTf)2 and N-methyl ephedrine can be conducted with reagent grade solvent containing 84-1000 ppm H2O. The products can be isolated in high yield and useful enantioselectivities (up to 99% ee).     

Enantioselective one-pot three-component synthesis of propargylamines catalyzed by copper(I)–pyridine bis-(oxazoline) complexes

A one-pot three-component coupling of aldehydes and amines in presence of terminal alkynes has been efficiently catalyzed by copper (I) complex of i-Pr-pybox-diPh 2b or s-Bu-pybox-diPh 2c. The process is simple and allows the synthesis of various propargylamines in good to excellent enantioselectivities (up to 99% ee) and in higher yields. The nature of the substituents attached to imines plays a vital role on the enantioselectivities obtained. The presence of gem-diphenyl group at C-5 position and secondary alkyl substituents at the C-4 chiral center of the oxazoline rings of the chiral ligands was found to be crucial for higher enantioselectivities. A transition state model involving π–π stacking is also proposed for the stereochemical outcome.     

Asymmetric syn-selective Henry reaction catalyzed by the sulfonyldiamine-CuCl-pyridine system

A catalytic asymmetric Henry reaction has been developed with use of a sulfonyldiamine-CuCl complex as a catalyst. A series of new binaphthyl-containing sulfonyldiamine ligands (2a-h) were readily synthesized in two steps starting from commercially available chiral 1,2-diamines. The (R,R)-diamine-(R)-binaphthyl ligand (2d)-CuCl complex smoothly catalyzed the enantioselective Henry reaction with the assistance of pyridine to give the corresponding adduct with high enantiomeric excess (up to 93%). Moreover, the 2d-CuCl-pyridine system promotes the diastereoselective Henry reaction in syn-selective manner to give the adduct in up to 99% yield with 92:8 syn/ anti selectivity. The enantiomeric excess of the syn-adduct was 84% ee.     

Catalytic asymmetric bromination and chlorination of beta-ketoesters

The first general catalytic asymmetric bromination and chlorination of beta-ketoesters has been developed. The reactions proceed for both acyclic and cyclic beta-ketoesters catalyzed by chiral bisoxazolinecopper(II) complexes giving the corresponding optically active alpha-bromo- and alpha-chloro-beta-ketoesters in high yields and moderate to good enantioselectivities. For the optically active chlorinated products the isolated yields are in the range of 88-99 % and the enantiomeric excesses up to 77 % ee, while the optically active brominated adducts are formed in 70-99 % isolated yield and up to 82 % ee. Based on the absolute configuration of the optically active products, the face selectivity for the catalytic enantioselective halogenation is discussed based on a bidentate coordination of the beta-ketoester to the chiral catalyst and a X-ray structure of chiral alpha,gamma-diketoesterenolatebisoxazolinecopper(II) complex.     

Gold(I)/Chiral N,N′‐Dioxide–Nickel(II) Relay Catalysis for Asymmetric Tandem Intermolecular Hydroalkoxylation/Claisen Rearrangement

A highly efficient asymmetric cascade reaction between alkynyl esters and allylic alcohols has been realized. Key to success was the combination of a hydroalkoxylation reaction catalyzed by a π‐acidic gold(I) complex with a Claisen rearrangement catalyzed by a chiral Lewis acidic N,N′‐dioxide–nickel(II) complex. A range of acyclic α‐allyl β‐keto esters were synthesized in high yields (up to 99 %) with good diastereoselectivities (up to 97:3) and excellent enantioselectivities (up to 99 % ee ) under mild reaction conditions. These products can be easily transformed into optically active β‐hydroxy esters, β‐hydroxy acids, or 1,3‐diols.     

Zinc-prolinamide complex catalyzed direct asymmetric aldol reactions in the presence of water

An efficient direct asymmetric aldol reaction with zinc triflate and prolinamides as combined catalysts is reported. A series of chiral prolinamides have been designed and used in the direct aldol reaction resulting in the desired products with excellent yields (up to 94% yield) and high enantioselectivities (up to 96% ee). Water was found to play a significant role in the formation of the aldol products, which suggests a new strategy in the design of new organic catalysts.     

Construction of Chiral Tetrahydro‐β‐Carbolines: Asymmetric Pictet–Spengler Reaction of Indolyl Dihydropyridines

A highly efficient synthesis of the enantioenriched tetrahydro‐β‐carbolines was developed by using a chiral phosphoric acid catalyzed Pictet–Spengler reaction of indolyl dihydropyridines. The reaction proceeds under mild reaction conditions to afford the desired chiral tetrahydro‐β‐carbolines in good to excellent yields (up to 96 %) and high enantioselectivities (up to 99 % ee ). With this method, a formal synthesis of tangutorine and a total synthesis of deplancheine were achieved in a highly efficient manner.     

Enantioselective synthesis of cis-1,2-disubstituted cyclopentanes and cyclohexanes by Suzuki-Miyaura cross-coupling and iridium-catalyzed asymmetric hydrogenation

A series of 1,2-disubstituted cyclohexene derivatives was prepared through Suzuki-Miyaura cross-coupling of 2-bromo-1-cyclohexenecarbaldehyde or 2-carbomethoxy-1-cyclohexen-1-yl triflate with arylboronates. These tetra-substituted cyclic alkenes were subjected to Ir-catalyzed asymmetric hydrogenation. In this way cis-1-methoxymethyl-2-arylcyclohexanes were obtained in high yield with excellent enantio- and diastereoselectivities (up to >99% ee, >99% cis) by using phosphinomethyloxazolines as ligands. Asymmetric hydrogenation of analogous cyclopentene derivatives, prepared by Suzuki-Miyaura cross-coupling, proved to be more difficult and proceeded with lower enantioselectivities of up to 88% ee. The synthetic potential of this cross-coupling/asymmetric-hydrogenation strategy was demonstrated by an enantioselective route to chiral hexahydrofluorenones.     

Enantioselective iridium-catalyzed hydrogenation of α-arylcinnamic acids and synthesis of (S)-equol

By using iridium catalyst based on chiral spiro phosphine–oxazoline ligands, the hydrogenation of α-arylcinnamic acids was accomplished under ambient pressure and low catalyst loading (as low as 0.01 mol %), providing useful 2,3-diarylpropionic acids in high yields with excellent enantioselectivities (up to 99% ee). A catalytic enantioselective synthesis of (S)-equol with the present hydrogenation reaction as a key step was accomplished starting from commercially available starting materials in six steps with 48.4% overall yield.     

Enantioselective pinacol coupling reaction of aromatic aldehydes catalyzed by chiral vanadium complexes

The asymmetric pinacol coupling of aromatic aldehydes by chiral salan–vanadium complexes as effective catalysts is reported. Chiral 1,2-diols were obtained with high diastereoselectivities (up to 90/10) and moderate to high enantioselectivities (up to 82% ee). The possible mechanism of the pinacol coupling reaction is also discussed.     

A recyclable organocatalyst for asymmetric Michael addition of acetone to nitroolefins

Based on different chiral diamine skeletons, a series of bifunctional primary amine-thiophosphoramides were synthesized and screened as the catalysts for the asymmetric Michael addition of acetone to both aromatic and aliphatic nitroolefins. Under the catalysis of a thiophosphoramide derived from 1,2-diphenylethane-1,2-diamine, the corresponding adducts were obtained in high yields (up to >99%) with excellent enantioselectivities (97-99% ee) under mild reaction conditions. Moreover, the catalyst could be recovered via simple phase separation and reused at least five times without any loss of both catalytic activity and stereocontrol.