Chiral oxazoline-1,3-dithianes: new effective nitrogen–sulfur donating ligands in asymmetric catalysis

A series of new chiral oxazoline-1,3-dithianes has been easily synthesized and used as ligands for asymmetric catalysis. The conjugate addition of Et₂Zn to enones resulted in ees of up to 69%, whereas the Pd-catalyzed allylic alkylation led to the expected products in almost quantitative yields and up to 90% enantioselectivity. The ligand’s conformation has been explored using a combination of X-ray and NMR measurements, indicating the presence of a remarkable anomeric effect, which accounts for the preference of the oxazoline ring for the axial location.     

Aza-bis(oxazolines): new chiral ligands for asymmetric catalysis

Aza-bis(oxazolines) are introduced as chiral ligands for asymmetric catalysis combining the advantages of easy availability of bis(oxazolines) and backbone variability of aza-semicorrins. Especially, the title ligands could be attached to a polymeric support, which allowed the development of easily recoverable copper(I)-catalysts for asymmetric cyclopropanation reactions.     

P-Chirogenic diaminophosphine oxide: a new class of chiral phosphorus ligands for asymmetric catalysis

We successfully synthesized a novel P-chirogenic diaminophosphine oxide 4, which was applied to catalytic enantioselective construction of quaternary carbon centers using Pd-catalyzed asymmetric allylic substitution with various beta-keto esters (up to 99% yield, 94% ee). Preliminary mechanistic studies indicated that two molecules of 8 coordinate to the Pd metal in a monodentate fashion, resulting in the formation of Pd complex 9 (Pd:8 = 1:2), which functions as the active species.     

Chiral bicyclic phosphoramidites--a new class of ligands for asymmetric catalysis

The development of new ligands for catalytic asymmetric C-C bond formation is of great interest to organic synthesis. We describe here a new class of chiral phosphoramidites that embody one or two binaphthol units attached to an achiral azabicyclic [3.3.1] or [3.3.0] framework. These ligands were easily accessible from (R)1,1'-binaphthyl-2,2'-dioxaphosphorchloridite (4) and the corresponding heterobicyclic core 1, 2, or 3. They were employed in enantioselective Cu-catalyzed additions of different dialkylzinc reagents to cyclic and acyclic enones. The chiral ketones were obtained with an enantiomeric ratio up to 91:9. The choice of the best ligand proved to be strongly dependent on each substrate. In addition, ligand 6 was found to be the most suitable for Rh-catalyzed hydrogenations of a,beta-unsaturated esters, giving rise to dimethyl 2-methylsuccinate and methyl N-acetylalaninate with enantiomer ratios up to 95:5.     

Enantiomerically pure phenanthroline or bipyridine containing macrocycles: a new class of ligands for asymmetric catalysis

New enantiomerically pure phenanthroline- and bipyridine-containing macrocycles have been synthesized by combination of the coordinating unit to inexpensive and readily available chiral templates. The catalytic properties of their Cu(I) complexes have been studied in the cyclopropanation of alkenes as test reaction. A simple structural modification of the chiral cavity allowed us to successfully control the trans or cis diastereoselectivity of the reaction.     

C2-symmetric bis-hydrazones as ligands in the asymmetric Suzuki-Miyaura cross-coupling

Glyoxal bis-hydrazone derived from (S,S)-1-amino-2,5-diphenylpyrrolidine behaves as an excellent ligand for phosphine-free, asymmetric Suzuki-Miyaura cross couplings, thereby affording a variety of enantiomerically enriched biaryls with different substitution patterns. The high catalytic activity of the [PdCl2(bis-hydrazone)] complex allows reactions to be performed at room temperature, affording products with excellent enantioselectivities in all cases.     

Novel sulfinyl imine ligands for asymmetric catalysis

[structure: see text] A novel class of P,N-sulfinyl imine ligands has been prepared that incorporates chirality solely at sulfur. The Pd complex of ligand 14 catalyzes the allylic alkylation reaction with high enantioselectivity (94%), and the first crystal structure of a Pd-bound sulfinyl imine provides insight into binding mode and origins of stereoselectivity.     

The synthesis of new planar chiral heterobidentate chelate ligands for asymmetric catalysis

A series of new heterobidentate N,S; N,O and N,P chelate ligands have been synthesised where the sole source of chirality is derived from a planar chiral ferrocene unit and have been shown to give up to 79% ee (R) in the palladium catalysed allylic substitution reaction, suggesting that they may be suitable in other palladium catalysed processes.     

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.     

BINEPINES: chiral binaphthalene-core monophosphepine ligands for multipurpose asymmetric catalysis

The atropisomeric structure of 4,5-dihydro-3H-dinaphtho[2,1-c;1',2'-e]phosphepine is the common axially chiral scaffold of a library of monophosphine ligands nicknamed BINEPINES that have shown a quite remarkable stereoselection efficiency in a broad variety of enantioselective reactions involving the formation of new C-H or C-C or C-X bonds. In this critical review the properties and scope of this type of chiral ligands are illustrated (70 references).     

Synthesis, resolution and racemisation studies of new tridentate ligands for asymmetric catalysis

A method for the high-yielding preparation of two tridentate, isoquinoline-derived ligands, involving successive Suzuki cross-coupling reactions, is described. The first ligand could be resolved via molecular complexation with N-benzylcinchonidinium chloride, while the second was resolved by chromatographic separation of its epimeric camphorsulfonates. The barrier to rotation about the central biaryl axis was evaluated via racemisation studies, and the absolute configuration assigned by X-ray crystallography.     

Chiral phosphine-phosphoramidite ligands in asymmetric catalysis

Chiral phosphine-phosphoramidite ligands, featuring ready availability, easy modification, and stability towards air and moisture, have recently emerged as a new kind of robust ligands for asymmetric catalysis. They have been found to display wide utilities in various catalytic asymmetric reactions, giving excellent enantioselectivities in the Rh-, Ru-, and Ir-catalyzed asymmetric hydrogenation of C?C, C?O, and C?N double bonds; Rh-catalyzed asymmetric hydroformylation; Pd-catalyzed asymmetric hydrophosphorylation; Pd-catalyzed asymmetric allylic alkylation; Ag-catalyzed asymmetric [3 + 2] cycloaddition; and Cu-catalyzed conjugate addition and reduction. In this review, the progress on the development of chiral phosphine-phosphoramidite ligands in asymmetric catalysis has been summarized.     

Chiral monophosphines as ligands for asymmetric organometallic catalysis

Chelating chiral diphosphines are often used as ligands of organometallic complexes. However monophosphines, or more generally ligands with one phosphorus linked to one or several heteroatom, may also be useful. This review gives the main results obtained in that area, by considering the classes of monodentate chiral ligands bearing one P(III) atom and involved in asymmetric catalysis with organometallic complexes.     

手性胺膦配体在不对称催化中的应用

利用邻二苯基膦苯甲醛分别与多种手性二胺的缩合反应,设计合成了一系列新型手性四齿胺膦配体.这类多齿胺膦配体含有两个软的磷原子和两个硬的氮原子,具有丰富的配位化学性能和优秀的不对称诱导能力.本文综述了手性胺膦金属络合物催化剂在不对称转移氢化反应、氧化动力学拆分反应、烯烃的不对称环氧化反应和不对称环丙烷化反应、不对称D-A反应中的应用.     

Novel nitrogen ligands based on imidazole derivatives and their application in asymmetric catalysis

Recently prepared chiral amines have been used in the preparation of novel tridentate ligands based on an imidazole ring with an additional (hetero)ring. The synthesis was carried out by the reaction of chiral amines with suitable aldehydes (2-phenylimidazole-4-carbaldehyde, 2-hydroxybenzaldehyde or pyridine-2-carbaldehyde) under reductive conditions (H₂/Pd or NaBH₄). All ligands prepared showed strong hydrogen bonds in d₆-DMSO solution, which resulted in hindered imidazole tautomerism. The observed hindered tautomerism was studied by ¹H NMR spectroscopy. The structures of the prepared ligands were also confirmed by APCI mass spectroscopy. Both chiral amines and tridentate compounds have been applied as ligands in copper (II)-catalyzed nitroaldol reactions (Henry reaction). Various reaction conditions for the Henry reaction have been studied (influence of temperature, molar ratio, solvent or copper (II) precursors). The compounds prepared with the two imidazole rings showed fast reaction times and a reversal in enantioselectivity compared to other chiral amines.     

Synthesis and application of phosphinoferrocenylaminophosphine ligands for asymmetric catalysis

A new class of bidentate ligands utilizing a phosphine-aminophosphine structure has been prepared on a ferrocenylethyl backbone in a straightforward and scalable fashion from acetylferrocene. The unique property of the alpha-ferrocenyl carbonium ion that allows the replacement of a variety of "leaving groups" with retention of configuration greatly facilitates the synthesis, and a number of ligands have been prepared by varying the nitrogen and phosphorus substituents on the aminophosphine. These readily prepared phosphinoferrocenylaminophosphines, known as BoPhoz ligands, show surprising hydrolytic and air stability, with no degradation after 3 years open to the air. The rhodium complexes of these ligands show exceedingly high enantioselectivities (generally >95% ee) and activities often in excess of 50,000 catalyst turnovers per hour for the asymmetric hydrogenation of a wide variety of dehydro-alpha-amino acid and itaconic acid derivatives. They also show high activity and good to excellent enantioselectivity for the hydrogenation of a number of alpha-ketoesters.     

A new class of readily available and conformationally rigid phosphino-oxazoline ligands for asymmetric catalysis

A new class of conformationally rigid phosphino-oxazoline ligands 3 were synthesized via an efficient ortho-substitution of phenyl glycinol as the key step. Divergent synthetic routes for easy ligand modulation, as well as a procedure suitable for scale-up synthesis, were established. The catalytic potential of ligands 3 has been demonstrated in the highly enantioselective Ir-catalyzed hydrogenation of alkenes and Pd-catalyzed allylic substitution and intermolecular Heck reactions.     

糖骨架手性配体合成及应用于不对称催化反应研究进展

获得对映异构体纯的手性化合物在药物、农用化学品、香料等领域愈来愈引起了科学界和工业界的广泛关注.不对称催化反应作为获得光学纯化合物的一种有效手段,由于其手性增殖的突出优势而特别引人注目.不对称催化一般通过含有手性配体