手性茂金属催化剂在不对称硅氢化反应中的应用

手性茂金属催化剂在不对称硅氢化反应中的应用研究近扯为取得了很大进展。对９０年代以来具有高手性诱导效应的手性二茂铁络合催化剂及手性二茂钛系催化剂进行了重点评述,并展望了其应用研究前景。     

Photoswitchable Chiral Organocatalysts: Photocontrol of Enantioselective Reactions

This study presents recent advances in photoswitchable chiral organocatalysts and their applications in the photomodulation of enantioselective reactions. Under irradiation with an appropriate wavelength of light, the E/Z-photoisomerization of the photoresponsive units on the catalysts leads to the control of the catalytic activity and/or selectivity of the enantioselective reactions. Additionally, this study elucidates the design, synthesis, and catalytic application of the fabricated azobenzene BINOL-based photoswitchable chiral phase-transfer catalysts. This account will provide insights into the appropriate design of a photoswitchable chiral organocatalyst that can achieve both good enantioselectivity and photocontrol.     

手性伯胺催化剂用于顺式选择性的不对称Cross-Aldol反应

基于酸碱作用,将手性伯胺与质子酸原位结合制得有机小分子催化剂,并用于醛与醛的不对称Cross-aldol反应.与一般手性仲胺催化剂不同,该类伯胺催化剂得到的是顺式选择性构型的Cross-aldol产物,其产率达90%,顺反比和ee值分别为9:1和90%.相比而言,采用简单易得的(1S,2S)-(+)-环己二胺即可得到较高选择性的顺式产物.     

Chiral Bisphosphoric Acids and Their Applications in Asymmetric Catalysis

Asymmetric Brønsted acid catalysis has been recognized as a powerful concept for asymmetric synthesis. In the process of pursuing more robust and highly effective chiral Brønsted acid catalysts, chiral bisphosphoric acids have received much attention in the last two decades. Their unique catalytic properties are mainly attributed to the inherent intramolecular hydrogen bonding interactions that could increase the overall acidity and tune the conformation property. Integrating hydrogen bonding into the catalyst design, quite a few structurally unique and effective bisphosphoric acids have been synthesized, which frequently exhibited superior selectivity in a broad range of asymmetric transformations. This review summarizes the status quo of chiral bisphosphoric acid catalysts and their applications in catalyzing asymmetric transformations.     

Synthesis of Chiral Aldehyde Catalysts by Pd‐Catalyzed Atroposelective C−H Naphthylation

Chiral aldehyde catalysis opens new avenues for the activation of simple amines. However, the lack of easy access to structurally diverse chiral aldehyde catalysts has hampered the development of this cutting‐edge field. Herein, we report a Pd‐catalyzed atroposelective C?H naphthylation with 7‐oxabenzonorbornadienes for the preparation of axially chiral biaryls with excellent enantioselectivities (up to >99 % ee). This reaction is scalable and robust, which serves as a key step to provide a rapid access to axially chiral aldehyde catalysts through a three‐step C?H functionalization sequence. These chiral aldehydes exhibit better activities and enantioselectivities than the previously reported organocatalysts in the asymmetric activation of glycine derived amides and dipeptides. Moreover, preliminary investigation also discloses that the aldehyde catalyst can effectively override the intrinsic facial selectivity of chiral dipeptide substrates, showcasing the strong chiral induction ability of this type of novel aldehyde catalysts.     

Catalytic Enantioselective Olefin Metathesis in Natural Product Synthesis. Chiral Metal‐Based Complexes that Deliver High Enantioselectivity and More

Chiral olefin metathesis catalysts enable chemists to access enantiomerically enriched small molecules with high efficiency; synthesis schemes involving such complexes can be substantially more concise than those that would involve enantiomerically pure substrates and achiral Mo alkylidenes or Ru‐based carbenes. The scope of research towards design and development of chiral catalysts is not limited to discovery of complexes that are merely the chiral versions of the related achiral variants. A chiral olefin metathesis catalyst, in addition to furnishing products of high enantiomeric purity, can offer levels of efficiency, product selectivity and/or olefin stereoselectivity that are unavailable through the achiral variants. Such positive attributes of chiral catalysts (whether utilized in racemic or enantiomerically enriched form) should be considered as general, applicable to other classes of transformations.     

Understanding the Reactivity and Selectivity of Fluxional Chiral DMAP-Catalyzed Kinetic Resolutions of Axially Chiral Biaryls

Fluxional chiral DMAP-catalyzed kinetic resolutions of axially chiral biaryls were examined using density functional theory. Computational analyses lead to a revised understanding of this reaction in which the interplay of numerous non-covalent interactions control the conformation and flexibility of the active catalyst, the preferred mechanism, and the stereoselectivity. Notably, while the DMAP catalyst itself is confirmed to be highly fluxional, electrostatically driven π⋅⋅⋅π⁺ interactions render the active, acylated form of the catalyst highly rigid, explaining its pronounced stereoselectivity.     

The role of achiral pyrazolidinone templates in enantioselective Diels-Alder reactions: scope, limitations, and conformational insights

We have evaluated the role of achiral pyrazolidinone templates in conjunction with chiral Lewis acids in room temperature, enantioselective Diels-Alder cycloadditions. The role of the fluxional N(1) substituent was examined, with the bulky 1-naphthylmethyl group providing enantioselectivities up to 99% ee, while templates with smaller fluxional groups gave lower selectivities. High selectivities were also observed in reactions of 7d with chiral Lewis acids derived from relatively small chiral ligands, suggesting the pyrazolidinone templates are capable of relaying stereochemical information from the ligand to the reaction center. Lewis acids capable of adapting square planar geometries, such as Cu(OTf)2, Cu(ClO4)2, and Pd(ClO4)2, were found to be particularly effective at providing high selectivities. Additionally, substitution at the C-5 position of the pyrazolidinone templates has been shown to be critical for optimal selectivity. Reactions of the optimal pyrazolidinone appended with a number of common dienophiles and various dienes demonstrate the utility of this achiral template. Furthermore, catalytic loadings could be lowered to 2.5 mol % with essentially no loss in selectivity. Pi-Pi interactions were evaluated as a means to explain the unusually high selectivity observed at room temperature. Finally, non-C2-symmetric ligands were employed as a test to determine if chiral relay was operative.     

手性双哌啶衍生物用于甲基三氧化铼催化烯烃不对称环氧化反应

以N-烷基-4-哌啶酮为原料,制备了几个手性双哌啶衍生物配体.以尿素-过氧化氢复合物(UHP)为氧化剂,甲醇为溶剂,将这些配体用于甲基三氧化铼(MTO)催化的前手性烯烃的环氧化反应,考察了各种反应参数对催化剂催化性能的影响.结果表明,手性双哌啶衍生物的加入可降低MTO的催化活性,但可提高环氧化物的选择性;这些配体对前手性烯烃的环氧化反应有较低的手性诱导作用,对映体过量值(ee值)只有4%-11%.讨论了对映选择性低的原因.     

Highly Enantioselective Diels-Alder Reactions Promoted by Non C2-Symmetric Chiral Ligands

Ligand design and synthesis occupy a central theme in asymmetric catalysis. [1] In developing chiral ligands, their design should provide an opportunity for tuning through easy modification of substituents. In a large number of cases, this means starting from a new chiral source. We have been interested in design/synthesis of novel chiral ligands that allow for diversity to be introduced with ease. We have designed a new ligand system containing a core dihydropyrazole moiety with chiraliuy residing remotely to the fluxional group as shown in Scheme 1. There are three points of diversity and these are indicated on the structure.     

Applications of Intramolecular Cyclopropanations of Chiral Secondary Allylic Diazoacetates

The diastereomeric secondary allylic diazoacetates 6a,b and 8a,b , which were readily prepared from the common intermediate 4 , were cyclized in the presence of the achiral catalyst Cu(TBS)₂ to furnish mixtures of the adducts 9a,b/10a,b and 12a,b/13a,b , respectively; in these cyclizations, the diastereoselectivity of the reaction was substrate controlled. When 6a,b and 8a,b were cyclized in the presence of the chiral catalysts Rh₂[(5S)‐MEPY]₄ or Rh₂[(5R)‐MEPY]₄, the substrate‐based selectivity could be reversed if the chirality of the substrate and catalyst were matched. The advantages associated with the use of chiral catalysts to effect the diastereoselective cyclization of chiral allylic diazoacetates were demonstrated by the synthesis of 25 , which comprises the cyclopropane subunit found in the diterpene ingol B ( 14 ).     

不对称diels-Alder反应中的手性催化剂

本文综述了近年来不对称Diels-Alder反应中手性催化剂研究的进展,对各类手性催化剂的性能和特点作了简要介绍.     

Atroposelective Synthesis of Axially Chiral N-Arylpyrroles by Chiral-at-Rhodium Catalysis

A transformation of fluxional into configurationally stable axially chiral N-arylpyrroles was achieved with a highly atroposelective electrophilic aromatic substitution catalyzed by a chiral-at-metal rhodium Lewis acid. Specifically, N-arylpyrroles were alkylated with N-acryloyl-1H-pyrazole electrophiles in up to 93 % yield and with up to >99.5 % ee, and follow-up conversions reveal the synthetic utility of this new method. DFT calculations elucidate the origins of the observed excellent atroposelectivity.     

修饰型多相手性催化剂在不对称合成中的应用

本文评述了修饰型多相手性催化剂在不对称合成中的应用。按照不同的制备方法及催化反应对一些多相催化体系进行了归类总结, 包括过渡金属手性配合物的固相化、修饰型手性固体催化剂、手性分子筛及嵌入型粘土手性催化剂。对酒石酸及金鸡纳碱修饰型金属催化剂的反应机理也进行了探讨。     

Chiral hetero- and carbocyclic compounds from the asymmetric hydrogenation of cyclic alkenes

Several types of chiral hetero- and carbocyclic compounds have been synthesized by using the asymmetric hydrogenation of cyclic alkenes. N,P-Ligated iridium catalysts reduced six-membered cyclic alkenes with various substituents and heterofunctionality in good to excellent enantioselectivity, whereas the reduction of five-membered cyclic alkenes was generally less selective, giving modest enantiomeric excesses. The stereoselectivity of the hydrogenation depended more strongly on the substrate structure for the five- rather than the six-membered cyclic alkenes. The major enantiomer formed in the reduction of six-membered alkenes could be predicted from a selectivity model and isomeric alkenes had complementary enantioselectivity, giving opposite optical isomers upon hydrogenation. The utility of the reaction was demonstrated by using it as a key step in the preparation of chiral 1,3-cis-cyclohexane carboxylates.     

An Efficient Approach to Chiral Allyloxyamines by Stereospecific Allylation of Nitrosoarenes with Chiral Allylboronates

A novel and efficient approach to allyloxyamines by the allylation of nitrosoarenes with α‐chiral allylboronates is described. C? O bond formation occurs with high stereospecificity and the product allyloxyamines are easily transformed into valuable chiral building blocks such as isoxazolidines and allylic alcohols. The reaction features complete regioselectivity (O‐selectivity), high E/Z selectivity, and excellent chirality transfer.     

Atroposelective Synthesis of Axially Chiral N‐Arylpyrroles by Chiral‐at‐Rhodium Catalysis

A transformation of fluxional into configurationally stable axially chiral N‐arylpyrroles was achieved with a highly atroposelective electrophilic aromatic substitution catalyzed by a chiral‐at‐metal rhodium Lewis acid. Specifically, N‐arylpyrroles were alkylated with N‐acryloyl‐1H‐pyrazole electrophiles in up to 93 % yield and with up to >99.5 % ee, and follow‐up conversions reveal the synthetic utility of this new method. DFT calculations elucidate the origins of the observed excellent atroposelectivity.     

Chiral amines as organocatalysts for asymmetric conjugate addition to nitroolefins and vinyl sulfones via enamine activation

Over the last decade the potential of organocatalysis has successfully been demonstrated. In particular, chiral amines such as pyrrolidine analogues have emerged as a broadly applicable class of organocatalyst for asymmetric conjugate addition via enamine activation. This Feature Article documents the development of these catalysts, emphasizing the design and mechanistic features that supply high selectivity in asymmetric Michael reactions.     

手性亚砜合成*

手性亚砜及其衍生物广泛作为重要手性中间体和辅剂、手性配体和催化剂、手性药物。手性亚砜可以采用生物方法和化学方法来合成,化学方法包括手性辅剂诱导、手性氧化剂氧化、手性拆分和不对称催化等。本文简要综述了手性亚砜的各种用途和各种合成方法的研究进展,主要介绍了钛和钒催化的不对称硫醚氧化反应,也介绍了作者最近在钒催化的不对称硫醚氧化反应方面所做的研究工作。     

Enhanced Photocatalytic Hydrolysis Performance of Chiral Molecule Loaded Titanium Disulfide Nanosheets

The photoelectrochemical (PEC) water decomposition is a promising method to produce hydrogen from water. To improve the water decomposition efficiency of the PEC process, it is necessary to inhibit the generation of H₂O₂ byproducts and reduce the overpotential required by cheap catalysts and a high current density. Studies have shown that coating the electrode with chiral molecules or chiral films can increase the hydrogen production and reduce the generation of H₂O₂ byproducts. This is interpreted as the result of a chiral induced spin selectivity (CISS) effect, which induces a spin correlation between the electrons that are transferred to the anode. Here, we report the adsorption of chiral molecules onto titanium disulfide nanosheets. Firstly, titanium disulfide nanosheets were synthesized via thermal injection and then dispersed through ultrasonic crushing. This strategy combines the CISS with the plasma effect caused by the narrow bandgap of two-dimensional sulfur compounds to promote the PEC water decomposition with a high current density.