Organocatalytic Asymmetric Synthesis of an Advanced Intermediate of (+)-Sarain A

The first organocatalytic asymmetric synthesis of an advanced intermediate of (+)-sarain A was achieved. This approach featured the employment of an organocatalytic asymmetric Michael addition reaction and a nitrogen-to-carbon chirality transfer to forge three chiral centers, as well as a catalytic hydrosilylation for the chemoselective reduction of a key lactam intermediate. The tricyclic intermediate contained all the required functionalities for elaborating into (+)-sarain A.     

光学活性沙丁胺醇的不对称合成研究进展

综述了不对称反应合成光学活性沙丁胺醇的研究进展。其中包括手性辅基诱导、不对称硼氢化、不对称催化氢化、不对称转移氢化、不对称双羟基化反应、酶催化的不对称氰醇化反应等。     

Hydrogen diffusion transfer through an asymmetric three-layer vanadium membrane

Hydrogen diffusion transfer through a three-layer membrane has been studied within the framework of the lattice model under the Bragg?Williams approximation. A set of equations describing hydrogen transfer through a vanadium membrane coated with thin palladium layers has been derived taking into account the interactions of hydrogen atoms in the membrane layers. The obtained equations have been solved using the Mathcad-14 software package. It has been shown that the interaction between hydrogen atoms has a significant influence on hydrogen permeability at near-atmospheric pressures. It has been found that the permeability of the vanadium membrane is markedly higher than that of a palladium one at the same thickness. The effect of asymmetric vanadium membrane embrittlement has been shown to depend on the location of palladium layers with different thicknesses. The embrittlement of the vanadium membrane begins at higher pressures, when a thicker palladium layer is located at the inlet. It has been revealed that, for asymmetric membranes, the value of the diffusion flux of hydrogen atoms may depend on the transfer direction. At the same membrane thickness, the permeability of the asymmetric membrane is actually equal to that of a symmetrical membrane, provided that a thicker palladium layer is located at the inlet. At the opposite orientation, of the permeability of the asymmetric membrane is lower than that of the symmetric one.     

Chirality transfer during alkylation of chiral amides

Chiral amides derived from O-methyl mandelic acid and achiral amines underwent enantioselective alpha-methylation on treatment with LTMP followed by addition of methyl iodide; chirality transfer from an undeprotonated chiral amide into an achiral enolate in a mixed aggregate is supposed to be responsible for the asymmetric induction.     

Utilizing an o‐Quinone Methide in Asymmetric Transfer Hydrogenation: Enantioselective Synthesis of Brosimine A,Brosimine B,and Brosimacutin L

A concise and highly enantioselective synthesis of the flavonoids brosimine A, brosimine B, and brosimacutin L is reported for the first time. The key transformation is a single‐step conversion of a flavanone into a flavan by means of an asymmetric transfer hydrogenation/deoxygenation cascade.     

D-葡萄糖衍生物在不对称催化反应中的研究进展

D-葡萄糖手性衍生物, 在不对称催化反应中的研究进展十分迅速, 综述了近年来D-葡萄糖手性衍生物直接作为催化剂催化不对称相转移Michael加成反应、氢硅烷化自由基链反应等和作为催化剂配体在不对称环氧化、氰硅烷化及Reformatsky等反应中的应用进展.     

Asymmetric transfer hydrogenation using amino acid derivatives; further studies and a mechanistic proposal

A series of investigations into the use of amino acid derivatives for the asymmetric catalysis of the transfer hydrogenation of ketones are presented. Based on the results observed, a mechanistic suggestion for the origin of the enantioselective induction is proposed.     

聚醚树枝体线性聚(N-异丙基丙烯酰胺)不对称嵌段共聚物的 合成及自组装

采用原子转移聚合方法合成了聚N-异丙基丙烯酰胺和聚醚树技体的不对嵌段共聚物Dendr.PE-PNI-PAM。实验结果表明Dendr.PE-PNIPAM分子在水中能通过疏水缔合作用形成具有双分子膜结构的超分子聚集体。临界缔合浓度(CAC)、聚集体的大小及形貌对树枝体的代数具有明显的依赖关系。该聚集体对温度刺激具有响应性,并在人体体温温度(37.5℃)发生相转变。在高于相转变温度时,Dendr.PE-PNIPAM分子形成管状、带状等多重形态的超级结构的聚集体。     

联二萘酚衍生手性磷酸在亚胺不对称转移氢化反应中的应用研究进展

综述了BINOL衍生手性磷酸在亚胺不对称转移氢化反应中的应用研究进展。根据亚胺不对称转移氢化反应中三类不同的氢供体--Hantzsch酯类氢源、2-取代苯并噻唑啉类氢源及其他氢源,对BINOL衍生手性磷酸催化的亚胺不对称转移氢化反应进行了重点介绍。参考文献５３篇。     

Axially Chiral Imidodiphosphoric Acid Catalyst for Asymmetric Sulfoxidation Reaction: Insights on Asymmetric Induction

Insights into chiral induction for an asymmetric sulfoxidation reaction involving a single oxygen atom transfer are gained through analyzing the stereocontrolling transition states. The fitting of the substrate into the chiral cavity of a new class of imidodiphosphoric Brønsted acids, as well as weak C H⋅⋅⋅π and C H⋅⋅⋅O noncovalent interactions, are identified as responsible for the observed chiral induction.     

Investigation of the photoinduced energy transfer in the supramolecular complexes of styryl dyes

Self-assembly of monostyryl dye of benzothiazole series with symmetric and asymmetric bisstyryl dyes based on dibenzo-18-crown-6 ether has been studied by optical and NMR spectroscopies. The photoinduced energy transfer between monoand bisstyryl dyes in supramolecular assembly has been analyzed. The cascade energy transfer in the supramolecular complex of monostyryl dye with asymmetric bisstyryl dye has been suggested.     

过渡金属配合物在不对称合成中的催化应用

综述了过渡金属配合物在不对称氢化、不对称环丙烷化、不对称环氧化等不对称合成中的催化应用以及最新的进展。参考文献35篇。     

Design of novel polymer-supported chiral catalyst for asymmetric transfer hydrogenation in water

New polymer-supported chiral sulfonamides containing sulfonated pendant group have been synthesized. Chiral catalyst prepared from the new polymer-support is more effective for asymmetric transfer hydrogenation of aromatic ketones in water compared to that prepared from conventional polystyrene-support. Polymer-supported catalysts containing quaternary ammonium salt as a pendant increased not only the reactivity but also the enantioselectivity in asymmetric transfer hydrogenation in water. Moreover, this type of polymer can be reused without loss of the catalytic activity.     

A concise,asymmetric synthesis of tetramic acid derivatives

[reaction: see text] A simple, asymmetric synthesis of tetramic acid derivatives is described in this paper. The key step is a carbonyl transfer from carbonyldiimidazole (CDI) to alpha-diimines (I) to form N-alkyl-4-alkylamino-5-methylenepyrrol-2-ones (II). In turn, these compounds can be easily transformed into tetramic acid derivatives (III) in two additional steps.     

Vibrational coherence transfer characterized with Fourier-transform 2D IR spectroscopy

Two-dimensional infrared (2D IR) spectroscopy of the symmetric and asymmetric C[Triple Bond]O stretching vibrations of Rh(CO)(2)acac in hexane has been used to investigate vibrational coherence transfer, dephasing, and population relaxation in a multilevel vibrational system. The transfer of coherence between close-lying vibrational frequencies results in extra relaxation-induced peaks in the 2D IR spectrum, whose amplitude depends on the coherence transfer rate. Coherence transfer arises from the mutual interaction of the bright CO stretches with dark states, which in this case reflects the mutual d-pi(*) back bonding of the Rh center to both the terminal carbonyls and the acetylacenonate ligand. For 2D IR relaxation experiments with variable waiting times, coherent dynamics lead to the modulation of peak amplitudes, while incoherent population relaxation and exchange results in the growth of the relaxation-induced peaks. We have modeled the data by propagating the density matrix with the Redfield equation, incorporating all vibrational relaxation processes during all three experimental time periods and including excitation reorientation effects arising from relaxation. Coherence and population transfer time scales from the symmetric to the asymmetric stretch were found to be 350 fs and 3 ps, respectively. We also discuss a diagrammatic approach to incorporating all vibrational relaxation processes into the nonlinear response function, and show how coherence transfer influences the analysis of structural variables from 2D IR spectroscopy.     

Asymmetric autocatalysis: product recruitment for the increase in the chiral environment (PRICE)

Asymmetric catalytic reactions are possible via efficient transfer of the chiral environment of a reaction to the transition state. In theory any asymmetric structure may contribute to this, including the product of the reaction itself. For product influence to be significant, a nonlinear effect needs to operate, whereby one diastereomer of the product/catalyst assists the reaction, and the other does not. When these conditions are satisfied, we obtain an asymmetric autocatalytic reaction in which the enantiomeric excess of a compound (that is both product and catalyst) actually increases as the reaction iterates. It is only recently that we have seen reports of such processes. Of particular interest are Soai's reports of the alkylation of aromatic heterocycles. Such reactions, aside from their inherent interest, may offer clues into the origins of asymmetric molecular replication that predated the origin of life.     

Synthesis of polymer microspheres functionalized with chiral ligand by precipitation polymerization and their application to asymmetric transfer hydrogenation

Monodisperse, crosslinked poly(divinylbenzene) and poly(methacrylic acid‐co‐ethylene glycol dimethacrylate) microspheres with (1R,2R)‐N¹‐toluenesulfonyl‐1,2‐diphenylethylene‐1,2‐diamine ((R,R)‐TsDPEN) moiety were successfully prepared by precipitation polymerization. Introduction site of the (R,R)‐TsDPEN moiety into the polymer microspheres could be controlled by changing the order of addition of the corresponding monomers. The functionalized polymer microspheres were applied to asymmetric transfer hydrogenation of ketone and imine. Polymer microsphere‐supported chiral catalysts showed good reactivity and enantioselectivity in the catalytic asymmetric transfer hydrogenations. Chiral secondary alcohol was quantitatively obtained with 94% ee in the asymmetric transfer hydrogenation of acetophenone in water. We also found that introduction site of the chiral catalyst and hydrophobicity of the microspheres, as well as degree of the crosslinking, affected the yield and enantioselectivity of chiral product in this reaction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3340–3349, 2010     

Ground and excited state double hydrogen transfer in symmetric and asymmetric potentials: comparison of 2,7,12,17-tetra-n-propylporphycene with 9-acetoxy-2,7,12,17-tetra-n-propylporphycene

Analysis of time-resolved anisotropy of transient absorption enabled determination of room temperature ground and excited state rate constants for intramolecular double hydrogen transfer in two similar porphycenes, one of them with symmetric and the other, with asymmetric character of a double minimum potential for hydrogen motion. The perturbation preserves a quasi-symmetric minimum in S(0), but the rate decreases approximately two times. In S(1), the perturbed potential becomes strongly asymmetric, and the downhill hydrogen transfer occurs with a rate higher than that observed for a symmetrical compound.     

Chiral DMAP‐N‐oxides as Acyl Transfer Catalysts: Design,Synthesis, and Application in Asymmetric Steglich Rearrangement

A DMAP‐N‐oxide, featuring an α‐amino acid as the chiral source, was developed, synthesized and applied in asymmetric Steglich rearrangement. A series of O‐acylated azlactones afforded C‐acylated azlactones possessing a quaternary stereocenter in high yields (up to 97 % yield) and excellent enantioselectivities (up to 97 % ee). Compared to the widespread use of pyridine nitrogen, which serves as the nucleophilic site in the asymmetric acyl transfer reaction, we discovered that chiral DMAP‐N‐oxides, in which the oxygen now acts as the nucleophilic site, are efficient acyl transfer catalysts. Our finding might open a new door for the development of chiral DMAP‐N‐oxides for asymmetric acyl transfer reactions.