Chiral and diastereoisomeric rhodium(I) coordination compounds with carvone as bidentate ligand

The chiral dienone p-mentha-6,8-dien-2-one (carvone) coordinates readily with rhodium(I) to form complexes of pronounced stability. Novel diastereoisomeric planar coordination compounds of rhodium(I) containing two chiral bidentate ligands have been prepared for the first time. The synthesis of the compounds is simple, and the yields are high.     

N-Phosphano nitrogen-containing five-membered aromatic chiral α-sulfoxides as new chiral ligands in asymmetric palladium-catalyzed allylic alkylation: stereoelectronic effects of the substituents on the aromatic rings

New chiral ligands, N-diphenylphosphano nitrogen-containing five-membered aromatic compounds bearing chiral sulfinyl groups as the sole chiral source has been developed. The structure of a palladium intermediate derived from the new chiral sulfoxide ligand was determined as a palladium complex with a five-membered chelate ring formed by coordination of the phosphano group and the sulfinyl sulfur atom involved. The stereoelectronic effects of substituents on the aromatic rings are discussed.     

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.     

Chiral eighteen-component three-dimensional supramolecular entities stabilized by the hydrogen bonding and coordination interactions

A new class of chiral eighteen-component three-dimensional supramolecular entities has been assembled in toluene and chloroform from twelve zinc porphyrin-appended 2-(ethylamino)- pyrimido[4,5-b][1,8]naphthyridin-4(3H)-one monomers and six chiral bipyridyl compounds. The heterocyclic segments form two C₆-symmetric cyclic hexamers, which are stabilized by a well-established DDA-AAD hydrogen bonding motif, while the six chiral bispyridine ligands are coordinated to the corresponding zinc porphyrin units to give the two-layered architectures. The structures have been characterized by the ¹H NMR, UV-vis and circular dichroism experiments, which also reveals that, when the concentration of the monomers is high enough, the chiral supramolecular entity can be formed exclusively.     

The use of mixtures of ligands in the Ir-catalyzed asymmetric reductive amination of 6-methyl-2,3,4,9-tetrahydro-1<Emphasis Type="Italic">H</Emphasis>-carbazol-1-one

A comparative testing of complex catalysts with homo and hetero combinations of chiral and achiral monodentate phosphite- and phosphine-type ligands in the Ir-catalyzed asymmetric direct reductive amination of 2,3,4,9-tetrahydro-1H-сarbozol-1-ones was carried out. A positive effect of the use in the reaction of a mixture of chiral and achiral ligands was demonstrated. This approach makes feasible a one-pot synthesis of valuable biologically active compounds of (tetrahydro-1H-carbazol-1-yl)amine series.     

Synthesis of chiral sulfinamido-sulfonamides and their evaluation as ligands for the enantioselective ethylation of aldehydes

A family of chiral sulfinamido-sulfonamide ligands have been synthesized from sulfinimines and has been evaluated as ligands for the enantioselective addition of diethylzinc to aldehydes with Ti(OⁱPr)₄. The structure of these diamino compounds has been systematically modified to optimize the results.     

Asymmetric synthesis of novel 1,4-aminoalcohol ligands with norbornene and norbornane backbone: use in the asymmetric diethylzinc addition to benzaldehyde

The asymmetric synthesis of cis-1,4-aminoalcohols with norbornene and norbornane backbone was performed starting with (2S,3R)-(−)-cis-hemiester 1 (98% ee). Chemoselective amination with HMPTA followed by Grignard reactions and subsequent LAH reductions afforded compounds 5a–d. cis-Hemiester 1 was also transformed into chiral ligands 7a–f and 9a–d with the DCC coupling method followed by LAH reduction using acyclic, heterocyclic amines and various aniline derivatives and p-toluenesulfonamide, respectively. The chiral ligands were subjected to asymmetric diethylzinc addition to examine their effectiveness as chiral catalysts. Among these, arylamine and tosyl substituted chiral ligands 9a–d exhibited the highest selectivities (up to 97% ee).     

A chiral Rh–phosphite complex displaying high activity in the enantioselective Rh-catalyzed addition of arylboronic acids to carbonyl compounds: when and why atropos is better than tropos

The use of deoxycholic acid derived tropos and atropoisomeric phosphites as chiral ligands in the Rh-catalyzed enantioselective addition of arylboronic acids to arylaldehydes and 2,2,2-trifluoroacetophenone is presented. Screening of these phosphites showed the high activity of the Rh-complex obtained starting from one of the two atropoisomeric ligands, which afforded complete conversion of the carbonyl compounds in short reaction times under mild reaction conditions and with ee’s of up to 84%. A study aimed at getting information about the different behavior of tropos and atropoisomeric ligands is also reported.     

Synthesis of two new chiral fluorous bis(oxazolines) and their applications as ligands in catalytic asymmetric reactions

Two new chiral fluorous bis(oxazolines) with a fluorous content of 56.9% and 59.3%, respectively, have been prepared starting from (S)-serine and (S)-tyrosine. Applications of these compounds as fluorous box ligands in asymmetric alkylations gave ees up to 92%, and in allylic oxidations ees up to 50%. Recycling and reuse of the ligands in asymmetric alkylation and of the catalytic system in allylic oxidation gave the same enantioselectivities.     

Synthetic control leading to chiral compounds

A highly diastereoselective cross aldol reaction is developed using divalent tin enolates formed from stannous trifluoromethanesulfonate and carbonyl compounds. The reaction is extended to a highly enantioselective cross aldol reaction employing chiral diamines derived from (S)-proline as ligands.     

Metal complexes with new types of chiral ligands based on natural terpenes

Some problems of the chemistry of coordination metal compounds with chiral ligands based on natural organic compounds, especially terpenes, are generalized. The results on the synthesis and study of the structure and properties of the chiral transition metal complexes with several groups of new “hybrid” ligands based on monoterpenes pinene, (+)-3-carene, and limonene and sesquiterpene caryophyllene are considered.     

Synthesis of phosphorylated sulfoximines and sulfinamides and their application as ligands in asymmetric metal catalysis

Starting from inexpensive materials and following simple protocols various N-phosphorylated sulfoximines and sulfinamides have been synthesized. The newly prepared compounds were then applied as chiral ligands in asymmetric transition metal catalysis. Phosphorus triamide-type ligands derived from (S)-glutamic acid were found to be the most efficient stereoselectors in enantioselective palladium-catalyzed allylic substitutions (up to 97% ee). On the other hand, diamidophosphite-type structures stemming from (S)-proline were the best ligands in rhodium-catalyzed hydrogenation reactions (up to 84% ee).     

金属催化的不对称氢化反应研究进展与展望

手性过渡金属络合物催化的不对称氢化反应是合成光学活性化合物的重要方法. 本文从手性配体及手性催化剂、不对称催化新反应、新方法和新策略三个方面简要评述新世纪以来过渡金属催化的不对称氢化反应研究领域的新进展. 从新世纪初至今, 手性单磷配体得到了复兴, 出现了如MonoPhos、SiPhos、DpenPhos等高效单齿亚磷酰胺酯配体; 磷原子手性(P-手性)配体也得到了快速发展, 如BenzP*、ZhanPhos、TriFer等已成为新的高效手性双膦配体; 螺环骨架手性配体成为新世纪手性配体设计合成的亮点, 除了SiPhos、SIPHOX、SpinPHOX等高效手性螺环配体外, 手性螺环吡啶胺基磷配体SpiroPAP的铱催化剂成为目前最高效的分子催化剂. 不对称催化氢化新反应研究也取得了突破, 如非保护烯胺、杂芳环化合物及N-H亚胺的氢化等反应都实现了高对映选择性. 自组装手性催化剂、树枝状手性催化剂、铁磁性纳米负载的可回收手性催化剂, 以及“混合”配体手性催化剂等新方法和新策略也在不对称催化氢化反应中得到了应用. 然而, 手性过渡金属络合物催化的不对称氢化研究仍然充满挑战, 也期待新的突破.     

Asymmetric Suzuki–Miyaura Cross‐Coupling for the Synthesis of Chiral Biaryl Compounds as Potential Monophosphine Ligands

Efficient asymmetric Suzuki–Miyaura coupling reactions have been employed for the first time to synthesize chiral biaryl compounds with phosphinate groups as chiral auxiliaries. A series of functionalized chiral biaryls are thereby synthesized in excellent yields and good diastereoselectivities (up to >95:5 d.r.) and axially chiral monophosphorus ligands are obtained through further functionalizations.     

New chiral thiols and C2-symmetrical disulfides of Cinchona alkaloids: ligands for the asymmetric Henry reaction catalyzed by CuII complexes

Seven Cinchona alkaloids were reacted with thioacetic acid and Bu₃P/diethyl diazadicarboxylate in THF at 0–25 °C to give the corresponding thiolacetates with complete inversion of configuration at the substitution center. The thus obtained chiral thiolesters were converted into thiols and these compounds were oxidized to the respective disulfides of C₂-symmetry. Both C-9 thioles and disulfides were tested as chiral ligands in the Cu-catalyzed asymmetric Henry reaction. When the thiol derivatives of an 8,9-like configuration were applied in the reaction of benzaldehyde and nitromethane, the obtained nitroaldol was of the same absolute configuration as the catalyst and the observed enantioselectivity was up to 83% ee. These ligands gave higher ees than the corresponding thioethers, disulfides, and thioles of 8,9-unlike configuration. The results obtained are in agreement with the proposed transition-state model involving nucleophilic attack of a deprotonated nitromethane directed preferably at one side of the O-complexed benzaldehyde.     

Diamagnetic lanthanide tris β-diketonate complexes with aryl-containing ligands as chiral NMR discriminating agents

Diamagnetic lanthanum(III) and lutetium(III) tris β-diketonate complexes with the aryl-containing ligands 3-benzoyl-(+)-camphor and 3-(2-naphthoyl)-(+)-camphor are effective organic-soluble chiral NMR discriminating agents for oxygen- and nitrogen-containing compounds. Enantiomeric discrimination of sufficient magnitude to determine the enantiomeric purity is observed in the ¹H NMR spectra of compounds with hydroxyl, carbonyl, oxazolidinone, amine, and sulfoxide groups. Diamagnetic lanthanide complexes with the aryl-containing β-diketonate ligands are almost always more effective than those with 3-trifluoroacetyl-(+)-camphor, 3-heptafluorobutyryl-(+)-camphor, and d,d-dicampholylmethane that have been previously reported. Many hydrogen atoms of the substrates are significantly shielded in the presence of the lanthanide chelates with the aryl-containing ligands, which likely enhances the extent of enantiomeric discrimination in the NMR spectra. No combination of metal and ligand is most effective for all substrates. Larger enantiomeric discrimination is usually observed in benzene-d₆ or cyclohexane-d₁₂ than in chloroform-d. Diamagnetic lanthanide tris β-diketonates with the aryl-containing ligands provide an alternative to paramagnetic chelates that often cause too much broadening in the ¹H NMR spectrum.     

Iridium-catalyzed asymmetric hydrogenation of 3-substituted unsaturated oxindoles to prepare C3-mono substituted oxindoles

An efficient and enantioselective hydrogenation of 3-substituted unsaturated oxindoles has been developed by an iridium complex of tropos phosphine-oxazoline ligands. It is the first example to prepare chiral C3-mono substituted oxindoles via asymmetric catalysis. And the reaction provides instant access to this kind of compounds with excellent conversion and enantioselectivities (up to 93% ee).     

Enantioselective hydrogenation of (Z)- and (E)-β-arylenamides catalyzed by rhodium complexes of monodentate chiral spiro phosphorous ligands: a new access to chiral β-arylisopropylamines

A highly enantioselective rhodium-catalyzed hydrogenation of both (Z)- and (E)-β-arylenamides was developed by using monodentate chiral spiro phosphite and phosphine ligands, respectively. The hydrogenation reaction provides an efficient access to optically active β-arylisopropylamines, important building blocks for the synthesis of biologically active compounds.     

Iridium complexes with P-stereogenic phosphino imidazole ligands: Synthesis,structure and catalysis

The synthesis of optically and diastereomerically pure P-stereogenic phosphine-imidazole ligands is reported. The new ligands contain either a benzoimidazole or a 4-phenylimidazole as a N-donor fragment. The ligands have been coordinated to iridium and the structure of the corresponding cationic COD complexes has been determined by X-ray analysis. The combination of the chiral phosphorus atom and the imidazole substituents generate a strong chiral environment around the metal center. Preliminary hydrogenation reactions with a model cyclic β-enamide are also reported.     

A Dynamic Kinetic Resolution Approach to Axially Chiral Diaryl Ethers by Catalytic Atroposelective Transfer Hydrogenation

Diaryl ethers are widespread in biologically active compounds, ligands and catalysts. It is known that the diaryl ether skeleton may exhibit atropisomerism when both aryl rings are unsymmetrically substituted with bulky groups. Despite recent advances, only very few catalytic asymmetric methods have been developed to construct such axially chiral compounds. We describe herein a dynamic kinetic resolution approach to axially chiral diaryl ethers via a Brønsted acid catalyzed atroposelective transfer hydrogenation (ATH) reaction of dicarbaldehydes with anilines. The desired diaryl ethers could be obtained in moderate to good chemical yields (up to 79 %) and high enantioselectivities (up to 95 % ee) under standard reaction conditions. Such structural motifs are interesting precursors for further transformations and may have potential applications in the synthesis of chiral ligands or catalysts.