Preparation of axially chiral biphenyl diphosphine ligands and their application in asymmetric hydrogenation

Axially chiral biphenyldiphosphine ligands bearing diphenylphosphino group(s) and/or dicyclohexylphosphino group(s) were prepared in enantiomerically pure form starting from 2,6-dimethylnitrobenzene via 8 steps: iodination, reduction, methoxylation through diazotization, Ullmann coupling, bromination, phosphorylation, optical resolution, and silane reduction, and the obtained ligands were used in rhodium-catalyzed asymmetric hydrogenation.     

Catechol-based phosphoramidites: a new class of chiral ligands for rhodium-catalyzed asymmetric hydrogenations

[reaction: see text] The synthesis and application of a new class of catechol-based phosphoramidites is described. Ees up to 99% were obtained in the rhodium-catalyzed asymmetric hydrogenation of dehydroamino acids and enamides.     

Design of chiral sulfoxide-olefins as a new class of sulfur-based olefin ligands for asymmetric catalysis

The design and development of a novel class of chiral sulfur-olefin hybrid ligands with high synthetic feasibility are described. These new sulfoxide-olefin ligands showed excellent catalytic activities and enantioselectivities (up to 98% ee) in rhodium-catalyzed asymmetric 1,4-addition reactions of aryl boronic acids to α,β-unsaturated carbonyl compounds.     

Synthesis of JOSIPHOS-type ligands via a diastereoselective three-component reaction and their application in asymmetric rhodium-catalyzed hydroborations

The recently reported diastereoselective three-component reaction for the synthesis of chiral propargylamines was used for a new stereoselective synthesis of JOSIPHOS-type ligands 2a–d. The present synthesis gives the desired diphosphines in good yields without the need of resolution. Ligands 2a–d were applied to the rhodium-catalyzed hydroboration of styrene.     

Synthesis of novel chiral phosphinocyrhetrenyloxazoline ligands and their application in asymmetric catalysis

Several novel planar chiral phosphinocyrhetrenyloxazolines have been synthesized, and their catalytic activities have been evaluated in a variety of asymmetric catalytic reactions. Preferable effects as compared to their ferrocenyl analogues have been observed in asymmetric allylic amination and asymmetric hydrosilylation, and up to 97% ee and 72% ee were reached, respectively. The Lewis basicity of the phosphorus on the ferrocene and the cyrhetrene, which contributes to their different behavior in catalysis, has been deduced by 31P NMR spectroscopy analysis, as indicated by 1J(77Se-31P) in the corresponding phosphine selenides.     

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.     

Convenient synthesis of a new class of chiral hydroxymethyldihydrooxazole ligands and their application in asymmetric addition of diethylzinc to aromatic aldehydes

A number of chiral hydroxymethyl-substituted dihydrooxazoles were synthesized from D-or L-mandelic acid and amino alcohols. The chiral ligands thus obtained were tested as catalyst in the asymmetric addition of diethylzinc to aromatic aldehydes, and the structure-activity relationship was studied. The addition products were characterized by an enantiomeric excess of up to 91%. Published in Zhurnal Organicheskoi Khimii, 2006, Vol. 42, No. 4, pp. 564–568. The text was submitted by the authors in English.     

Synthesis of a novel class of chiral N,N,N-tridentate pyridinebisimidazoline ligands and their application in Ru-catalyzed asymmetric epoxidations

A new class of easily tunable N,N,N-pyridinebisimidazoline (pybim) ligands have been synthesized. The synthesis and tunability of these chiral tridentate ligands are much easier and flexible compared to the popular pyboxes, making the former a suitable ligand tool box for various asymmetric transformations. Ruthenium complexes of the new ligands were synthesized and applied in the asymmetric epoxidation of olefins using hydrogen peroxide as the oxidant. Excellent yields and moderate to good enantioselectivities were achieved in the epoxidation of aromatic olefins.     

Preparation and application of chiral spiro nitrogen-containing ligands for cobalt-catalyzed asymmetric Michael addition

Two novel chiral spiro nitrogen-containing ligands, 7,7′-bis(2-pyridinecarboxamido)-1,1′-spirobiindane (abbreviated as SIPAD) and 7,7′-bis(2-quinolinecarboxamido)-1,1′-spirobiindane (abbreviated as SIQAD), were conveniently prepared from 1,1′-spirobiindane-7,7′-dicarboxylic acid in high yields (85% and 84%, respectively) in two steps. The cobalt complexes prepared in situ from Co(OAc)₂ and the ligands have been proven to be efficient catalysts for the asymmetric Michael addition reaction of malonates to chalcone derivatives. The alkylation products were obtained in high yields with moderate enantiomeric excesses under mild reaction conditions.     

Synthesis of enantiopure axially chiral C3-symmetric tripodal ligands and their application as catalysts in the asymmetric addition of dialkylzinc to aldehydes

The enantioselective synthesis of a novel-type C(3)-symmetric tripodal ligand that is composed of a central mesitylene-derived core and three functionalized, axially chiral biaryl subunits is described. The triol (M,M,M)-3 is a suitable catalyst for the enantioselective addition of dialkylzinc to various aromatic aldehydes with asymmetric inductions of up to 98% ee.     

Tunable dendritic ligands of chiral 1,2-diamine and their application in asymmetric transfer hydrogenation

Tunable dendritic N-mono-sulfonyl ligands have been designed and synthesized via direct N-mono-sulfonylization of the chiral dendritic vicinal diamines and their ruthenium complexes demonstrated high catalytic and recyclable activities with comparable enantioselectivities to Noyori–Ikariya’s TsDPEN-Ru in the asymmetric transfer hydrogenation of an extended range of substrates, such as ketones, keto esters, and olefins.     

Synthesis of novel BINOL-derived chiral bisphosphorus ligands and their application in catalytic asymmetric hydrogenation

Some novel ortho-substituted BINOL-derived bisphosphorous ligands (o-BINAPO and o-NAPHOS) were synthesis from readily available (S)-BINOL; these ligands showed excellent enantioselectivities (up to 99% ee) in Rh(I)-catalyzed asymmetric hydrogenation of functionalized olefins.     

Preparation of pyrrolidine-oxazoline containing ligands and their application in asymmetric transfer hydrogenation

Nine members of a new ligand class incorporating both an oxazoline ring and a pyrrolidine unit were prepared in an efficient four-step synthesis starting from readily available chiral amino alcohols and proline. A study of these ligands in the asymmetric transfer hydrogenation of acetophenone showed that the catalysts formed from [Ir(cod)Cl]₂ were the most active while those derived from [Ru(p-cymene)Cl₂]₂ gave the highest enantioselectivities (up to 61% ee).     

A new class of modular chiral ligands with fluxional groups

In ligand design for asymmetric catalysis, the usual norm is to derive the face shielding elements from a chiral source. New ligands in which the face shielding is determined by fluxional groups are introduced. Their design, modular synthesis, and experiments to demonstrate the significance of the fluxional groups are discussed. The advantage is that the fluxional groups, introduced at a later stage, allow for simple tuning of the face shielding group.     

Design and synthesis of new chiral phosphorus-olefin bidentate ligands and their use in the rhodium-catalyzed asymmetric addition of organoboroxines to N-sulfonyl imines

Novel chiral phosphorus-olefin bidentate ligands have been synthesized in a few steps from a readily available enantiopure compound. These ligands have been applied to a rhodium-catalyzed asymmetric addition of organoboroxines to N-sulfonyl aldimines, achieving high yield and enantioselectivity.     

N-Aryl indole-derived C–N bond axially chiral phosphine ligands: synthesis and application in palladium-catalyzed asymmetric allylic alkylation

N-Aryl indole-derived C–N bond axially chiral phosphine ligands 2a–c were obtained by DDQ oxidation of N-aryl indoline-derived phosphine oxide followed by silane reduction. Resolution of C–N bond atropisomers was achieved by chiral HPLC. The investigation of the rotation barrier for the C–N bond axial stability of phosphines and the determination of the absolute configuration of 2c are described. Finally, the ability of the chiral ligand 2c was demonstrated in a palladium-catalyzed asymmetric allylic alkylation (up to 99% ee).