Ruthenium-catalysed asymmetric hydrogenation of ketones using QUINAPHOS as the ligand

Highly enantioselective ruthenium-catalysed hydrogenation of aromatic ketones is achieved with (Ra,S(C))-QUINAPHOS in the presence of achiral and chiral diamines as co-catalysts.     

Rhodium-catalysed asymmetric hydrosilylation of ketones using HETPHOX ligands

The HETPHOX ligand class was applied to the rhodium-catalysed asymmetric hydrosilylation of a range of substituted acetophenones. Enantioselective hydrosilylation of acetophenone with the tert-butyl substituted HETPHOX ligand gave (R)-phenylethanol in excellent enantioselectivity (84% ee) and in good conversion (80%). When applied to the hydrosilylation of other ketones conversions up to 93% and enantioselectivities up to 88% were observed.     

Origins of enantioselectivity in the chiral diphosphine-ligated CuH-catalyzed asymmetric hydrosilylation of ketones

Computational investigations on the asymmetric hydrosilylation of acetophenone over ligated CuH catalysts were performed with the DFT method. The calculations predict that the catalytic reaction involves two steps: (1) CuH addition to the carbonyl group via a four-membered transition state (TS) with the formation of copper-alkoxide intermediates; (2) regeneration of the ligated CuH catalyst by an external SiH(4) through a metathesis process to yield the corresponding silyl ether. The calculations in the chiral diphosphine-ligated CuH systems suggest that the metathesis process is the rate-determining step (RDS). The CuH addition step is vital for the distribution of the racemic products and therefore represents the stereo-controlling step (SCT). In this step, the greater steric hindrance between the aromatic rings of the ligands and the substrate is identified as the major factor for enantioselectivity. The corresponding TS in the face-to-face mode, suffering less steric hindrance, is more stable than its analogue in the edge-to-face mode. The enantioselectivities are calculated to be related not only to the P-Cu-P bite angles in the stereo-controlling TSs, but also to the substituents at the P-aryl rings of the chiral ligands. In short, a larger P-Cu-P bite angle and suitably modified P-aryl rings together are necessary to achieve excellent ee values.     

Phosphorus-bearing axially chiral biaryls by catalytic asymmetric cross-cyclotrimerization and a first application in asymmetric hydrosilylation

A novel and efficient, two-step route to axially chiral biaryls is demonstrated. In a direct asymmetric cross-cyclotrimerization in the presence of a chiral cobalt(I) catalyst, axially chiral biaryls bearing phosphoryl moieties have been prepared, and through indirect evidence the authors have been able to clarify the origin of the stereochemical induction and the nature of the central intermediate in the catalytic cycle. By subsequent reduction of the phosphoryl moiety to the corresponding phosphine, a very efficient and atom-economical approach to chiral systems has been developed. These chiral systems clearly have great potential use as axially chiral monodentate P- or bidentate P,O-ligands, as has been demonstrated by the employment of the novel NAPHEP as a new monodentate acting ligand in an asymmetric hydrosilylation reaction.     

Evaluation of bifunctional chiral phosphine oxide catalysts for the asymmetric hydrosilylation of ketimines

A series of bifunctional phosphine oxides have been prepared and evaluated as catalysts for the trichlorosilane mediated asymmetric hydrosilylation of ketimines. bis-Phosphine oxides, hydroxy-phosphine oxides, and biaryl phosphine oxides all demonstrated good catalytic activity, but poor to moderate enantioselectivity. A bis-P-chiral phosphine oxide displayed the highest enantioselectivity of 60%.     

手性金属配合物催化的前手性羰基化合物的不对称硅 氢化反应研究进展

评述了近年来手性金属配合物催化的前手性羰基化合物的不对称硅氢化反应研究进展。     

催化不对称硅氧化反应研究进展

综述了催化不对称硅氢化反应的研究进展情况，重点介绍了最近十年来手性催 化剂配体的研究情况。     

Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes

Advances in the palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes are presented according to substrate types and chiral monophosphine ligands. Chiral monodentate phosphine ligands with a binaphthyl moiety have been proven to be the most efficient ligands for cyclic 1,3-dienes, and planar chiral ferrocenylmonophosphine ligands with two ferrocenyl moieties for linear 1,3-dienes. The ferrocenylmonophosphine ligands have expanded the substrate scope to 1,3-enynes in the asymmetric hydrosilylation. Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes and 1,3-enynes leads to the stereoselective synthesis of allylsilanes and allenylsilanes, respectively.     

Enantioselective metal complex catalysis. 6. Rhodium catalysts for asymmetric hydrosilylation based on chiral phosphites

A study has been made of the asymmetric hydrosilylation of acetophenone by diphenylsilane under the influence of rhodium complexes with chiral phosphites. The enantioselective nature of the reaction depends on the phosphite structure, the acetophenone/rhodium and ligana/rhodium ratios, and the temperature. The maximum optical yield (24%) is attainod on the complex [Rh(COD)Cl]₂/(S, S)-2-ethoxy-4,5-dicarbisopropoxy-1,3-2-dioxophiospholane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 983–989, May, 1991.     

Synthesis of chiral butenolides using amino-thiocarbamate-catalyzed asymmetric bromolactonization

The asymmetric cyclization of 4,4-disubstituted 3-butenoic acids is studied. Amino-thiocarbamates are used as the catalysts and N-bromosuccinimide is used as the stoichiometric halogen source. The resulting γ-butanolide products are readily converted into the corresponding γ-butenolides (up to 58% ee) derivatives in one-pot.     

Palladium-catalyzed asymmetric hydrosilylation of styrenes with trichlorosilane

Asymmetric hydrosilylation of styrenes with trichlorosilane catalyzed by palladium complexes coordinated with chiral monodentate phosphorus ligands produces chiral benzylic silanes, which can be converted into enantiomerically enriched benzylic alcohols by a stereospecific oxidative cleavage of the carbonsilicon bond with retention of configuration. Due to its high catalytic activity and perfect regioselectivity without producing any by-products, it has recently become a potent methodology to prove the efficacy of newly-developed chiral ligands, especially monodentate ones, in asymmetric synthesis.     

Ir-catalyzed asymmetric allylic amination using chiral diaminophosphine oxides

An Ir-catalyzed asymmetric allylic amination using chiral diaminophosphine oxide is described. Asymmetric allylic amination of terminal allylic carbonates proceeded in the presence of 2 mol % of Ir catalyst, 2 mol % of chiral diaminophosphine oxide, 5 mol % of NaPF₆, and BSA, affording the chiral branched allylic amines in up to 95% ee.     

Palladium-catalyzed asymmetric allylic alkylation using chiral aminophosphine ligands

Palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate 18 with a dimethyl malonate–BSA–LiOAc system has been successfully carried out in the presence of new chiral aminophosphine ligands 1–5 in good yields with good enantioselectivities (up to 85% e.e.).     

Synthesis of chiral binaphthalenes using the asymmetric Suzuki reaction

The synthesis of atropisomeric 1,1′-binaphthalenes can be achieved using an asymmetric Suzuki cross-coupling reaction. The Suzuki reaction leading to such hindered compounds is challenging and competing hydrolytic deboronation frequently dominates unless carefully chosen conditions are employed. The simple, standard mechanism is inadequate when describing the Suzuki coupling of hindered partners. Evidence suggests that the key step leading to asymmetry is transmetallation (delivery of the organometallic by the asymmetric ligand) and the reactions operate under kinetic control. Reductive elimination (itself likely to be triggered by oxidative addition of another molecule of halide) is fast compared with equilibration (epimerisation and/or cis-trans isomerisation).     

手性金属催化剂在不对称环丙烷化反应中的应用进展

手性金属催化剂在不对称环丙烷化反应中的应用一直是不对称合成领域的一个热点。对三十多年来的这一领域的手性金属催化剂的发展作了详细的归纳和评述。     

Catalytic asymmetric Michael reactions using a chiral rhodium complex

Catalytic asymmetric Michael reaction of β-keto esters and methyl vinyl ketone was achieved using a chiral diamine-based Rh complex to give the Michael adducts in up to 75% e.e.