Rhodium‐Catalyzed Highly Diastereo‐ and Enantioselective Synthesis of a Configurationally Stable S‐Shaped Double Helicene‐Like Molecule

An S‐shaped double helicene‐like molecule (>99 % ee), possessing stable helical chirality, has been synthesized by the rhodium(I)/difluorphos complex‐catalyzed highly diastereo‐ and enantioselective intramolecular double [2+2+2] cycloaddition of a 2‐naphthol‐ and benzene‐linked hexayne. The collision between two terminal naphthalene rings destabilizes the helical chirality of the S‐shaped double helicene‐like molecule, but the introduction of two additional fused benzene rings significantly increases the configurational stability. Thus, no epimerization and racemization were observed even at 100 °C. The enantiopure S‐shaped double helicene‐like molecule forms a trimer through the multiple C?H???π and C?H???O interactions in the solid‐state. The trimers stack to form columnar packing structures, in which neighboring stacks have opposite dipole directions. The accumulation of helical structures in the same direction in the S‐shaped double helicene‐like molecule enhanced the chiroptical properties.     

Rhodium-Catalyzed Enantioselective Synthesis,Structures, and Properties of Single and Double Azahelicene-Like Molecules

The enantioselective synthesis of aza[6] and [7]helicene-like molecules have been achieved by the cationic rhodium(I)/axially chiral biaryl bisphosphine complex-catalyzed intramolecular [2+2+2] cycloaddition of cyanodiynes. This protocol was successfully applied to the diastereo- and enantioselective synthesis of an S-shaped double aza[6]helicene-like molecule with a high ee value of 89 %. Although no epimerization and racemization were observed in the double carbo[6]helicene-like molecule at 80 °C, epimerization and racemization of the double aza[6]helicene-like molecule proceeded at 80 °C. This double aza[6]helicene-like molecule showed good fluorescent quantum yields and chiroptical responses under both neutral and acidic conditions.     

Rhodium-Catalyzed Enantioselective Synthesis of Highly Fluorescent and CPL-Active Dispiroindeno[2,1-c]fluorenes

The enantioselective synthesis of chiral [7]-helical dispirodihydro[2,1-c]indenofluorenes (DSF-IFs) was achieved for the first time in good yields with high er values (er up to 99 : 1). The crucial step of the whole reaction sequence was the enantioselective intramolecular [2+2+2] cycloaddition of tethered triynediols to indenofluorenediols, which was catalyzed by a Rh/SEGPHOS® complex. Further transformations led to the corresponding DSF-IFs. The prepared helically chiral DSF-IFs combine circularly polarized luminescence (CPL) activity (g_lum=∼10⁻³) with exceptionally high fluorescence quantum yields (up to Φ_lum=0.97).     

Rhodium‐Catalyzed Enantioselective [4+2] Cycloadditions of Vinylcarbenes with Dienes

The reaction of 2‐siloxycyclo‐1,3‐dienes with E‐vinyldiazoacetates in the presence of the bulky chiral dirhodium tetracarboxylate catalyst, Rh₂(R‐p‐PhTPCP)₄ results in an enantioselective [4+2] cycloaddition, in which three new stereogenic centers are formed. The [4+2] cycloadducts are generated as single diastereomers with high enantiocontrol (95–98 % ee). When the diene contains an additional stereogenic center, effective kinetic resolution can be achieved.     

New Types of Planar Chiral [2.2]Paracyclophanes and Construction of One‐Handed Double Helices

New types of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes were synthesized from racemic 4,12‐dihydroxy[2.2]paracyclophane as the starting compound. Regioselective dibromination and transformation afforded a series of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes, which can be used as chiral building blocks. In this study, left‐ and right‐handed double helical structures were constructed via chemoselective Sonogashira–Hagihara coupling. The double helical compounds were excellent circularly polarized luminescence (CPL) emitters with large molar extinction coefficients, good photoluminescence quantum efficiencies, and large CPL dissymmetry factors.     

邻羟基苄醇与邻羟基苯乙烯的催化不对称[4+2]环加成反应——手性色满骨架的立体选择性构建

研究了手性磷酸催化下邻羟基苄醇和邻羟基苯乙烯的不对称［4+2］环加成反应,立体选择性地一步构建了手性2,4-二取代四氢色满骨架,该反应具有较高的收率、中等到较高的对映选择性和很好的非对映选择性（最高产率为78%,最高ee值为72%,dr值基本都大于95∶5）.带有不同取代基的多种邻羟基苄醇和邻羟基苯乙烯均适用于该反应,电子效应对于该反应的对映选择性有一定影响,其中连有供电子基的底物具有更高的反应活性和对映选择性.由邻羟基苄醇原位生成的邻亚甲基苯醌中间体和邻羟基苯乙烯可以同时与催化剂手性磷酸形成双重氢键,对于促进反应的进行和控制该反应的对映选择性起着至关重要的作用.     

Rhodium-Catalyzed Asymmetric [2+2+2] Cycloaddition of 1,6-Enynes with Racemic Secondary Allylic Alcohols through Kinetic Resolution

It has been established that a cationic rhodium(I)/P-phos complex catalyzes the asymmetric [2+2+2] cycloaddition of 1,6-enynes with racemic secondary allylic alcohols to produce the corresponding chiral bicyclic cyclohexenes, possessing three stereogenic centers, as a single diastereomer with excellent ee values. Mechanistic experiments revealed that the present cycloaddition proceeds through the kinetic resolution of the racemic secondary allylic alcohols, in which one enantiomer preferentially reacts with the 1,6-enyne.     

Concerted Catalysis by Adjacent Palladium and Gold in Alloy Nanoparticles for the Versatile and Practical [2+2+2] Cycloaddition of Alkynes

A Pd‐Au alloy efficiently catalyzed the [2+2+2] cycloaddition of substituted alkynes. Whereas monometallic Pd and Au catalysts were totally ineffective, Pd‐Au alloy nanoparticle catalysts with a low Pd/Au molar ratio showed high activity to give the corresponding polysubstituted arenes in high yields. A variety of substituted alkynes participated in various modes of cycloaddition under Pd‐Au alloy catalysis. The Pd‐Au alloy catalysts exhibited high air tolerance and reusability.     

Design and Synthesis of Pyrrolidinyl Ferrocene-Containing Ligands and Their Application in Highly Enantioselective Rhodium-Catalyzed Olefin Hydrogenation

Herein, we report the design and synthesis of a series of chiral pyrrolidine-substituted ferrocene-derived ligands. The proficiency of this novel structural motif was demonstrated in the Rh-catalyzed asymmetric hydrogenation of dehydroamino acid esters and α-aryl enamides. The products were obtained with full conversions and excellent levels of enantioselectivities of up to >99.9% ee and 97.7% ee, respectively, using a BINOL-substituted phosphine-phosphoaramidite ligand which possesses planar, central, and axial chirality elements.     

Diastereo‐ and Enantioselective Palladium‐Catalyzed Dearomative [3+2] Cycloaddition of 3‐Nitroindoles

Diastereo‐ and enantioselective cycloaddition of 3‐nitroindoles with vinyl aziridine was realized under Pd‐catalysis using commercially available Walphos as the ligand, affording pyrroloindolines in high yields with high diastereo‐ and enantioselectivities. The reaction can be scaled up to a gram scale and the reaction products are easily converted to amino pyrroloindoline and other pyrroloindoline derivatives.     

Rhodium-Catalyzed Enantioselective [4+2] Cycloadditions of Vinylcarbenes with Dienes

The reaction of 2-siloxycyclo-1,3-dienes with E-vinyldiazoacetates in the presence of the bulky chiral dirhodium tetracarboxylate catalyst, Rh₂(R-p-PhTPCP)₄ results in an enantioselective [4+2] cycloaddition, in which three new stereogenic centers are formed. The [4+2] cycloadducts are generated as single diastereomers with high enantiocontrol (95–98 % ee). When the diene contains an additional stereogenic center, effective kinetic resolution can be achieved.     

Enantio‐ and Diastereoselective Synthesis of Chiral Allenes by Palladium‐Catalyzed Asymmetric [3+2] Cycloaddition Reactions

A protocol for the asymmetric synthesis of highly substituted chiral allenes with control of point and axial chirality has been developed. A palladium‐catalyzed [3+2] cycloaddition using readily available racemic allenes gives access to densely functionalized chiral allenes with excellent yields and functional group tolerance. The catalytic asymmetric protocol utilizes a broad range of allenyl TMM (trimethylenemethane) donors to form cyclopentanes, pyrrolidines, and spirocycles with very good control of regio‐, enantio‐, and diastereoselectivity. The chiral allene moiety is shown to be a valuable functional group for rapid elaboration towards complex targets.     

A Chiral N,N′‐Dioxide–ZnII Complex Catalyzes the Enantioselective [2+2] Cycloaddition of Alkynones with Cyclic Enol Silyl Ethers

A highly efficient enantioselective [2+2] cycloaddition between alkynones and cyclic enol silyl ethers was developed by using a chiral N,N′‐dioxide‐zinc(II) complex as a catalyst. This method functions well for a variety of terminal alkynes as well as cyclic enol silyl ethers, with good to excellent enantioselectivity (up to 97 % ee). This is also the first successful example for the catalytic enantioselective [2+2] cycloaddition of internal alkynes with cyclic enol silyl ethers to give fully substituted cyclobutenes. Meanwhile, the desired cyclobutene product can easily be transformed into fused cyclobutane derivatives.     

Catalytic Enantioselective Isocyanide-Based Reactions: Beyond Passerini and Ugi Multicomponent Reactions

The development of catalytic enantioselective isocyanide-based reactions is currently of great interest because the resulting products are valuable in organic synthesis, pharmacological chemistry, and materials science. This review assembles and comprehensively summarizes the recent achievements in this rapidly growing area according to the reaction types. Special attention is paid to the advantages, limitations, possible mechanisms, and synthetic applications of each reaction. In addition, a personal outlook on the opportunities for further exploration is given at the end.     

Palladium‐Catalyzed Asymmetric [4+3] Cyclization of Trimethylenemethane: Regio‐, Diastereo‐, and Enantioselective Construction of Benzofuro[3,2‐b]azepine Skeletons

The palladium‐catalyzed asymmetric [4+3] cyclization of trimethylenemethane donors with benzofuran‐derived azadienes furnishes chiral benzofuro[3,2‐b]azepine frameworks in high yields (up to 98 %) with exclusive regioselectivities and excellent stereoselectivities (up to >20:1 d.r., >99 % ee). This catalytic asymmetric [4+3] cyclization of Pd‐trimethylenemethane can enrich the arsenal of Pd‐TMM reactions in organic synthesis. In addition, this strategy provides an alternative approach to chiral azepines by a transition‐metal‐catalyzed asymmetric [4+3] cyclization.     

Catalytic Asymmetric Synthesis of Spirocyclic Azlactones by a Double Michael‐Addition Approach

Spirocyclic azlactones are shown to be useful precursors of cyclic quaternary amino acids, such as the constrained cyclohexane analogues of phenylalanine. These compounds are of interest as building blocks for the synthesis of artificial peptide analogues with controlled folds in the peptide backbone. They were prepared in the present study by a step‐ and atom‐economic catalytic asymmetric tandem approach, requiring two steps starting from N‐benzoyl glycine and divinylketones. The key of this protocol is the enantioselective formation of the azlactone spirocycles, which involves a Pd^II‐catalyzed double 1,4‐addition of an in situ generated azlactone intermediate to the dienone (a formal [5+1] cycloaddition). As the catalyst, a planar chiral ferrocene bispalladacycle was used. Mechanistic studies suggest a monometallic reaction pathway. Although the diastereoselectivity was found to be moderate, the enantioselectivity is usually high for the formation of the azlactone spirocycles, which contain up to three contiguous stereocenters. Spectroscopic studies have shown that the spirocycles often prefer a twist over a chair conformation of the cyclohexanone moiety.     

铟(I)/手性磷酸催化简单烯烃与β,γ-不饱和α-酮酸酯的不对称[4+2]环加成反应

报道了In（I）Cl/手性磷酸1a双酸体系催化的简单烯烃和β,γ-不饱和α-酮酸酯的不对称[4+2]环加成反应,可高产率、高选择性（最高99：1dr,99%ee）生成相应的exo-[4+2]环加成产物.InCl和磷酸的协同作用是反应成功的关键,单独使用InCl和磷酸都不能催化反应进行.