The application of chiral phosphine-Schiff base type ligands in silver(I)-catalyzed asymmetric vinylogous Mannich reaction of aldimines with trimethylsiloxyfuran

Catalytic asymmetric vinylogous Mannich (AVM) reactions of readily available aldimines with trimethylsiloxyfuran in the presence of catalytic amount of AgOAc and chiral phosphine-Schiff base type ligands are described, affording the corresponding products in up to 91% yield, anti/syn >99:1 and 81% ee.     

Cu(I)-catalyzed asymmetric α-hydroxylation of β-keto esters in the presence of chiral phosphine-Schiff base-type ligands

Chiral phosphine-Schiff base-type ligand L1 prepared from (R)-(?)-2-(diphenylphosphino)-1,1′-binaphthyl-2′-amine was found to be a fairly effective ligand for Cu(I)-promoted enantioselective α-hydroxylation of β-keto esters using oxaziridine 2a as the oxidant to give the corresponding products in high yields along with moderate enantioselectivities.     

Synthesis of planar chiral [2.2]paracyclophane monophosphine ligands and their application in the umpolung allylation of aldehydes

Chiral [2.2]paracyclophane monophosphines 8 were synthesized via resolution using chiral palladacycle 10. Chiral phosphinite 5 was also prepared from 4-hydroxy[2.2]paracyclophane. Phosphines 8 and phosphinite 5 were used as the ligand in the umpolung allylation of aldehydes 14 with cyclohexenyl acetate 15, giving homoallyl alcohols 16 in high diastereoselectivity and in moderate to good enantioselectivity. Palladacycle 10 was recovered by treating the palladacycle–phosphine complexes with sodium prolinate, followed by treatment with HCl in high yield.     

Ru(II)-catalyzed asymmetric cyclopropanation using chiral diphenylphosphino(oxazolinyl)quinoline ligands

Several chiral 8-diphenylphosphino-2-oxazolinylquinolines were synthesized starting from 2-cyano-8-hydroxyquinoline. These N,N,P-chelates were successfully employed in the Ru(II)-catalyzed asymmetric cyclopropanation reactions of diazo-alkenes. The catalytic system exhibited good reactivity and high thermal stability and provided high yields in the intramolecular cyclopropanation, albeit somewhat decreased enantioselectivities compared to known catalytic systems. A dramatic dependency of the enantioselectivity on the substituents of the oxazoline ring was observed.     

Mechanism and chemoselectivity of the Pd(II)-catalyzed allylation of aldehydes: a density functional theory study

Density functional theory calculations at the PBE1PBE/DGDZVP level of theory were performed to investigate the mechanism and chemoselectivity of Pd(II)-catalyzed allylation of aldehydes. The transfer of formaldehyde to the pi-allyl group of bis-pi-allylpalladium complex is a thermodynamically favored process (DeltaG = -1.4 kcal/mol), and its Gibbs free energy of activation (DeltaG) corresponds to 23.0 kcal/mol. Further support for the mechanism proposed herein, which requires the coordination of an aldehyde molecule to the metal center, comes from correctly predicting the chemoselectivity of the reaction when it is conducted with mixed bis-pi-allylpalladium complexes containing crotyl, methallyl, and 2-methoxyallyl groups.     

Catalytic asymmetric allylation of aldehydes via a chiral indium(III) complex

A chiral indium complex has been discovered to effect high enantioselectivities in the addition of allyltributyl stannanes to aldehydes. The allylation of a variety of aromatic, alpha,beta-unsaturated and aliphatic aldehydes resulted in good yields and high enantioselectivities (90-96% ee).     

Catalytic asymmetric allylation of aldehydes using the chiral (salen)chromium(III) complexes

The enantioselective addition of allylstannanes to glyoxylates and glyoxals, as well as simple aromatic and aliphatic aldehydes, catalyzed by chiral (salen)Cr(III) complexes, has been studied. The reaction proceeded smoothly for the reactive 2-oxoaldehydes and allyltributyltin in the presence of small amounts (1-2 mol %) of (salen)Cr(III)BF₄ (1b) under mild, undemanding conditions. However, in the case of other simple aldehydes, the use of high-pressure conditions is required to obtain good yields. Classic chromium catalyst 1b, easily prepared from the commercially available chloride complex 1a, affords homoallylic alcohols usually in good yield and with enantiomeric purity of 50-79% ee. The stereochemical results are rationalized on the basis of the proposed model.     

Direct synthesis of chiral tertiary diphosphines via Pd(II)-catalyzed asymmetric hydrophosphination of dienones

A highly diastereo- and enantioselective Pd(II)-catalyzed hydrophosphination of dienones with Ph(2)PH involving formation of double C*-P bonds has been developed, providing a series of chiral tertiary diphosphines (chiral PCP pincer ligands) in high yields. A catalytic cycle for the reaction was proposed.     

Evaluation of disaccharide-based ligands for Pd(0)-catalyzed asymmetric allylations

A series of phosphines based on disaccharides containing a d-glucosamine framework were prepared and tested for their abilities as ligands for the palladium(0)-catalyzed asymmetric allylic allylation of racemic 1,3-diphenyl-2-propenyl acetate with various nucleophiles. In contrast to previous results exploiting monosaccharides, the iminophosphines generally afforded higher enantiomeric excesses, up to 99%.     

Pd(II)-catalyzed asymmetric addition of malonates to dihydroisoquinolines

We have developed a highly efficient reaction for catalytic asymmetric addition of malonates to dihydroisoquinolines using chiral Pd(II) complexes. In the reactions, substrates with various substitution patterns were available, and the reactions were complete within several hours (<3 h in most cases) under mild reaction conditions, affording various optically active C1-substituted tetrahydroisoquinoline derivatives (up to 98% yield, up to 97% ee). Furthermore, slow addition of DDQ allowed the in situ generation of the reactive intermediate from the corresponding N-Boc-protected amine, and dehydrogenative addition reaction was successfully demonstrated.     

New Lewis-basic N-oxides as chiral organocatalysts in asymmetric allylation of aldehydes

Allylation of aromatic and heteroaromatic aldehydes 1a-k with allyltrichlorosilane 2 can be catalyzed by the new heterobidentate, terpene-derived bipyridine N-monoxides 4, 6a,b, and 8-11 (相似文献   

Development of chiral dinitrones as modular Lewis base catalysts: asymmetric allylation of aldehydes with allyltrichlorosilanes

Chiral dinitrones were synthesized by the condensation of a C₂-symmetrical chiral dihydroxylamine with various aldehydes. The electronic and steric properties of the dinitrones can be modified by changing the aldehyde component. The activity of dinitrones as Lewis base catalysts was examined for the asymmetric allylation of aldehydes with allyltrichlorosilanes. Using DMPU as an additive in chloroform, the reaction proceeded at room temperature to afford allylated products in good yields and good enantioselectivities.     

Palladium-catalyzed asymmetric allylic substitutions in the presence of chiral phosphine-imine type ligands

Chiral bidentate phosphine-imine type ligand L9 is fairly effective in the asymmetric allylic substitution of 1,3-diphenylpropenyl acetate with dimethyl malonate to give the corresponding adduct in moderate yield and good ee.     

Parallel synthesis of modular chiral Schiff base ligands and evaluation in the titatium(IV) catalyzed asymmetric trimethylsilylcyanation of aldehydes

Highly modular tridentate Schiff base ligands arising from enantiopure epoxyalcohols have been prepared and evaluated in catalysis using parallel methods. The key structural motifs and experimental parameters have been identified, allowing enantioselectivities of up to 77% ee in the titatium-catalyzed trimethylsilyl cyanide addition to aldehydes.     

Pd(0) or Pd(II)-catalyzed ring-opening reactions of benzylidene- and alkylidenecyclopropyl ketones and aldehydes

Pd(0) catalyzed reactions of methylenecyclopropyl carbonyl compounds afforded a convenient method for the synthesis of conjugate (E,E)-1,3-diene derivatives 2 in good to excellent yields. Moreover, we also found that Pd(II)-catalyzed reactions of methylenecyclopropyl carbonyl compounds with water gave 1,5-diketones in good to high yields via a carbene-palladium intermediate. The plausible reaction mechanisms have also been provided on the basis of control and ¹⁸O-labeling experiments.     

Pd(II)-catalyzed asymmetric Wacker-type cyclization for the preparation of 2-vinylchroman derivatives with biphenyl tetraoxazoline ligands

This article describes an efficient method for the preparation of chiral chroman derivatives by the Pd(II)-catalyzed asymmetric Wacker-type cyclization using a chelation-induced axially chiral tetraoxazoline ligand. Under the optimized conditions, up to 80% yield and up to 92% ee were obtained. This is the first example to utilize o-trisubstituted 3-butenylphenols as substrates in such transformation.     

Pd(II)-catalyzed decarboxylative allylation and Heck-coupling of arene carboxylates with allylic halides and esters

This work demonstrates an alternative method to prepare allylated arenes and aryl-substituted allylic esters via catalytic decarboxylative C-C bond formation using aromatic carboxylic acids and allylic halides and esters.     

Efficient Ru(II)-catalyzed asymmetric hydrogenation of simple ketones with C2-symmetric planar chiral metallocenyl phosphinooxazoline ligands

C₂-symmetric metallocenyl planar phosphinooxazoline ligands (2 and 3) have been applied in the Ru(II)-catalyzed asymmetric hydrogenation of simple ketones. This type of ligands enjoys the advantages of dual reaction sites as well as larger steric hindrance than their corresponding C₁-symmetric counterparts. As a result, almost quantitative conversions and excellent enantioselectivities were obtained for a series of simple ketones. Under the optimal reaction conditions, up to 99.7% ee was obtained in many cases. It was also confirmed that hydrogen rather than reaction solvent i-PrOH is at work in the hydrogenation procedure.     

Ruthenium(ii)-catalyzed regioselective 1,6-conjugate addition of umpolung aldehydes as carbanion equivalents

One of the most efficient and reliable approaches to construct C–C bonds involves the conjugate addition of carbon nucleophiles to electron-deficient ketones. Yet, 1,6-conjugate additions of extended conjugated systems largely remain underexplored due to difficulties in controlling the regioselectivity. Herein, we report umpolung aldehydes as carbanion equivalents for highly regioselective 1,6-conjugate addition reactions to unsaturated ketones, with preliminary studies of the enantioselective variant. The synergy of ruthenium(ii) catalyst and electron-rich, bidentate phosphine ligand is essential for the reactivity and selectivity under mild reaction conditions.

Highly regioselective 1,6-conjugate addition was developed using hydrazone as carbanion equivalent catalyzed by ruthenium under mild conditions.