New chiral phosphine–amide ligands in palladium-catalysed asymmetric allylic alkylations

Palladium-catalysed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate 8a with a dimethyl malonate–BSA–LiOAc system has been successfully carried out in the presence of new chiral phosphine–amide, such as 5, in good yields and high enantiomeric excesses of up to 85%.     

Preparation of new chiral pyrrolidinebisphosphines as highly effective ligands for catalytic asymmetric synthesis of R-(−)-pantolactone

New chiral pyrrolidinebisphosphines, MSCPM, PCPM and BCPM, were prepared. Among them, BCPM was found to be the most effective ligand for catalytic asymmetric synthesis of R-(−)-pantolactone.     

Novel carboncarbon bond formation induced by depalladation of organometallic compounds

Two internal alkynes undergo insertion at 20°C into the PdC bond of the cyclopalladated derivative of dimethylaminomethylferrocene to give new organometallic compounds. When the reaction with diphenylacetylene is performed at higher temperatures, depalladation occurs readily to give six- and seven-membered ortho-fused rings through new annulation reactions of phenyl groups, formation of one of these involving also the cleavage of a CN bond.     

Synthesis of chelating tertiary phosphine oxides via palladium-catalysed C–P bond formation

Bis(diphenylphosphine oxides) and bis(tert-butyl(phenyl)phosphine oxides) of 1,10-phenanthroline, 2,2′-bipyridine and pyridine were synthesised in good yields via the Pd(OAc)₂/dppf mediated cross-coupling reactions between 6,6′-dichloro-2,2′-bipyridine, 2,9-dichloro-1,10-phenanthroline, or 2,6-dichloropyridine and the corresponding secondary phosphine oxides. These compounds represent potential tetradentate chelating ligands for ions of f-block elements.     

Preparation of new chiral pyridine–phosphine ligands and their Pd-catalyzed asymmetric allylic alkylations

Enantiomerically pure 2-(diphenylphosphino)methyl-N-[1-(2-pyridinyl)ethyl]pyrrolidines 1 and 2 have been prepared by the stereospecific substitution of enantiomerically pure 1-(2-pyridinyl)ethyl methanesulfonate 6 with enantiomerically pure 2-(diphenylphosphino)methylpyrrolidine. Asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate 11 with dimethyl malonate sodium salt using the (S,S)-ligand 1 affords the (R)-product 12 with up to 86% e.e. in good yield.     

Efficient carboncarbon bond formation with thermally stable 1,1-dihalo-2,2,2-trifluoroethylzinc reagent

The zinc carbenoids CF₃CX₂ZnX, prepared from CF₃CX₃ and zinc powder in dimethylformamide, were found thermally stable to add to aldehyde carbonyls in excellent yields.     

α-Pinene-type chiral Schiff bases as tridentate ligands in asymmetric addition reactions

A group of tridentate Schiff bases derived from (+)-α-pinene were synthesized. The steric effects in the transition state, the importance of π-π stacking interactions as well as the electronic effects of aryl aldehydes according to Hammett constant values in the enantioselective addition of Et₂Zn to aldehydes with the use of Schiff bases as chiral ligands are described. Also, a variety of aldehydes were cyanated using a catalyst prepared in situ from titanium tetraisopropoxide and chiral Schiff bases. The influence of a conjugated double-bond in the cyanation substrates on enantioselectivity was observed. The chemical structures of the chiral Schiff base-titanium alkoxide complexes are discussed based on their ¹H and ¹³C NMR spectra. 3D models of the Zn₂-complex catalyst and Ti-complex catalyst containing α-pinane-type Schiff bases based on X-ray diffraction experiments are postulated. The models presented were consistent with the reported chirality of the addition product and observed ee.     

Asymmetric radical carboncarbon bond forming reactions in chiral amides and imides under sulfonyl groups stereocontrol

Asymmetric radical carbon–carbon bond formation was achieved in chiral amide and imide systems under sulfonyl group stereocontrol, providing high diastereoselectivity. The stereochemistry of the products was determined and the mechanism of the stereochemical pathways is rationalized by the formation of chelates of Lewis acid metals between oxygens of acetyl, amide, and imide carbonyls, or sulfonyl groups.     

Chiral furanoside phosphite–phosphoroamidites: new ligands for asymmetric catalytic hydroformylation

We have designed a new series of phosphite–phosphoroamidites ligands 1–4 based on a furanoside backbone. These ligands were screened in the Rh-catalyzed asymmetric hydroformylation of styrene, inducing high regioselectivities with 2-phenylpropanal and moderate enantioselectivities (up to 65% e.e.). The results showed that the configuration of the stereogenic carbon atom C(3) at the ligand backbone had remarkable effects on the activity and enantioselectivity. Replacing the tert-butyl substituents with methoxy substituents at the para positions of the biphenyl moieties improved the enantioselectivities. We have also studied the solution structures of HRh(PP)(CO)₂ complexes.     

Spiro indane-based phosphine–oxazoline ligands for palladium-catalyzed asymmetric arylation of cyclic N-sulfonyl imines

Palladium complexes of indane-based phosphine–oxazoline ligands with a spirocarbon stereogenic center were examined for asymmetric addition of arylboronic acids to cyclic N-sulfonyl imines. Excellent reaction activities (up to 99% yield) and enantioselectivities (up to 99% ee) were obtained with a broad scope of substrate.

     

Catalytic enantioselective carboncarbon bond formation by addition of dialkylzinc reagents to cyclic 1,3-diene monoepoxides

Chiral copper complexes of 2,2′-binaphthyl-based phosphorus amidites are shown to be highly effective catalysts for the conjugate addition of dialkylzinc reagents to vinyloxiranes. The corresponding allylic alcohol reaction products (S_N2′-pathway) were obtained with moderate to high regioselectivity. Both direct- (S_N2-pathway) and conjugate-opening addition (S_N2′-pathway) seem to proceed with complete anti stereoselectivity. The enantioselectivity of these addition reactions according to a kinetic resolution protocol turned out to be high (>90% ee) with 1,3-cyclohexadiene and 1,3-cycloheptadiene monoepoxides.     

Sterically congested, "roofed" β-iminodisulfides as new chiral ligands for palladium-catalyzed, asymmetric allylic alkylation

The preparation of a new class of "roofed" β-iminodisulfides from sterically congested, conformationally rigid chiral 2-thiazolidinones is described. A functional survey of palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate proved that symmetrical "roofed" β-iminodisulfides are efficient chiral ligands, showing enantioselectivity opposite that associated with chiral "roofed" β-iminothioether ligands.     

Design of a new class of chiral quinoline–phosphine ligands. Synthesis and application in asymmetric catalysis

The design and synthesis of a new class of chiral quinoline–phosphine ligands has been achieved. Their efficiency as asymmetric ligands in enantioselective palladium-catalyzed allylic substitution reactions and in the asymmetric copper-catalyzed addition of diethylzinc to enones was also investigated.     

A single phosphine ligand allows palladium-catalyzed intermolecular co bond formation with secondary and primary alcohols

Forging a bond: An efficient, general palladium catalyst for C?O bond-forming reactions of secondary and primary alcohols with a range of aryl halides has been developed using the ligand 1. Heteroaryl halides, and for the first time, electron-rich aryl halides can be coupled with secondary alcohols. A diverse set of substrate combinations are possible with just a single ligand, thus obviating the need to survey multiple ligands.     

A palladium complex immobilized onto mesoporous silica: a highly efficient and reusable catalytic system for carbon–carbon bond formation and anilines synthesis

A palladium complex supported on functionalized mesoporous silica MCM-41 proved to be a highly efficient, recoverable catalyst for C–C coupling reactions and amination of aryl halides to afford anilines. The nanocatalyst was characterized by FT-IR spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, N₂ adsorption–desorption isotherms and inductively coupled plasma analysis. The catalyst could be reused for several consecutive runs without significant loss of activity. The excellent yields of products, simple reaction procedures and short reaction times are the main advantages of this methodology.     

Palladium-catalyzed C–S bond formation by using N-amido imidazolium salts as ligands

N-Amido imidazolium salt was employed as a ligand in the palladium-catalyzed cross-coupling reaction of aryl halides and thiols, and showed good activity in the formation of thioether. The best combination for the coupling with aryl bromides was N-amido imidazolium salt 2 and NaHMDS, and that for the coupling with aryl iodides was N-amido imidazolium salt 1 and KO^tBu. The coupling reactions were conducted in the presence of Pd(OAc)₂ (1 mol %) in DMSO at 80 °C for 12 h.     

Metal-dependent stereochemistry of C—C bond formation under the asymmetric phase transfer catalysis by chiral salen complexes

The effect of the nature of the central metal atom in chiral salen type complexes on the stereodifferentiating capacity of these complexes as catalysts in phase transfer asymmetric alkylation of Schiff"s base derived from alanine isopropyl ester and benzaldehyde by benzyl bromide. The nature of the central metal atom in the complex has a pronounced influence on the stereochemistry of alkylation; copper(ii) complexes exhibit the highest activity combined with a high stereoselectivity.     

1,1′-Binaphthylazepine-based ligands for asymmetric catalysis. Part 2: New aminoalcohols as chiral ligands in the enantioselective addition of ZnEt2 to aromatic aldehydes

The new enantiopure 1,2-aminoalcohols 1b–1h having 1,1′-binaphthylazepine skeleton have been tested as catalytic precursors in the enantioselective addition of ZnEt₂ to benzaldehyde. The best results were seen with ligand 1d, which owes its chirality only to the atropisomerism of the binaphthyl nucleus and does not have any stereogenic carbon atom. In the presence of 1d benzaldehyde was quickly and cleanly transformed to (S)-1-phenylpropanol in 99% yield and 87% e.e. The same ligand was also used in the asymmetric ZnEt₂ addition to other aryl aldehydes giving rise to (S)-1-arylpropanols in almost quantitative yields and e.e.s up to 90%.     

Synergistic chiral ion pair catalysts for asymmetric catalytic synthesis of quaternary α,β-diamino acids

The combination of a chiral phosphate anion with a silver ion has been demonstrated as a powerful and synergistic ion pair catalyst for the aza-Mannich reaction. A series of valuable quaternary α,β-diamino acid derivatives was obtained in high yield, and with excellent diastereo- (up to 25:1 dr) and enantioselectivity (up to 99% ee). The adducts can be smoothly transformed into the corresponding protected chiral quaternary α,β-diamino acids by a one-pot hydrolysis reaction.