Aminated Ordered Mesoporous Carbons: Preparation and Catalytic Performance for Knoevenagel Condensation Reactions

The amine‐ and diamine‐functionalized mesoporous carbons with hexagonal mesostructure have been prepared by a rationally two‐step modification procedure under mild reaction conditions, respectively. The physicochemical properties of the obtained solid basic mesoporous catalysts were characterized by XRD, TEM, N₂ adsorption‐desorption, FT‐IR, EDX and elemental analysis techniques. The results indicated the organic amine groups were successfully introduced inside the channels of mesoporous carbons without destroying the well‐ordered 2D hexagonal mesostructure. A series of Knoevenagel condensation of aldehyde/ketone with active methylene compounds have been carried out over the diamine‐function‐ alized mesoporous carbons, which proved to be efficient heterogeneous basic catalysts and exhibited a similar catalytic activity after sixth cycles. This can be attributed to its hydrophobic framework and hydrophilic diamine groups, which led to amphiphilic properties and offered some advantages for the Knoevenagel condensation reactions.     

Unprecedented Selectivity of Ruthenium Iodide Benzylidenes in Olefin Metathesis Reactions

The development of selective olefin metathesis catalysts is crucial to achieving new synthetic pathways. Herein, we show that cis‐diiodo/sulfur‐chelated ruthenium benzylidenes do not react with strained cycloalkenes and internal olefins, but can effectively catalyze metathesis reactions of terminal dienes. Surprisingly, internal olefins may partake in olefin metathesis reactions once the ruthenium methylidene intermediate has been generated. This unexpected behavior allows the facile formation of strained cis‐cyclooctene by the RCM reaction of 1,9‐undecadiene. Moreover, cis‐1,4‐polybutadiene may be transformed into small cyclic molecules, including its smallest precursor, 1,5‐cyclooctadiene, by the use of this novel sequence. Norbornenes, including the reactive dicyclopentadiene (DCPD), remain unscathed even in the presence of terminal olefin substrates as they are too bulky to approach the diiodo ruthenium methylidene. The experimental results are accompanied by thorough DFT calculations.     

Iodonium Metathesis Reactions

A metathesis reaction occurs when a diaryliodonium triflate is heated with an aryl iodide, resulting in the formation of a new diaryliodonium triflate.     

Toward Metathesis Reactions on Vinylphosphaalkenes

Abstract

Attempts to utilize C-ethylenic phosphaalkenes in metathesis reactions are discussed. Unprecedented reactivity is observed where the vinylphosphaalkene undergoes the first step of the catalytic cycle and cross-metathesis with the phenylmethylene moiety of Grubbs 2nd generation catalyst. However, homo-metathesis reaction to form 1,6-diphosphahexa-1,3,5-triene is not observed, presumably due to steric constraints.     

Classical Keggin Intercalated into Layered Double Hydroxides: Facile Preparation and Catalytic Efficiency in Knoevenagel Condensation Reactions

The family of polyoxometalate (POM) intercalated layered double hydroxide (LDH) composite materials has shown great promise for the design of functional materials with numerous applications. It is known that intercalation of the classical Keggin polyoxometalate (POM) of [PW₁₂O₄₀]^3? (PW₁₂) into layered double hydroxides (LDHs) is very unlikely to take place by conventional ion exchange methods due to spatial and geometrical restrictions. In this paper, such an intercalated compound of Mg_0.73Al_0.22(OH)₂ [PW₁₂O₄₀]_0.04?0.98 H₂O (Mg₃Al‐PW₁₂) has been successfully obtained by applying a spontaneous flocculation method. The Mg₃Al‐PW₁₂ has been fully characterized by using a wide range of methods (XRD, SEM, TEM, XPS, EDX, XPS, FT‐IR, NMR, BET). XRD patterns of Mg₃Al‐PW₁₂ exhibit no impurity phase usually observed next to the (003) diffraction peak. Subsequent application of the Mg₃Al‐PW₁₂ as catalyst in Knoevenagel condensation reactions of various aldehydes and ketones with Z‐CH₂‐Z′ type substrates (ethyl cyanoacetate and malononitrile) at 60 °C in mixed solvents (V_2‐propanol:V_water=2:1) demonstrated highly efficient catalytic activity. The synergistic effect between the acidic and basic sites of the Mg₃Al‐PW₁₂ composite proved to be crucial for the efficiency of the condensation reactions. Additionally, the Mg₃Al‐PW₁₂‐catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate demonstrated the highest turnover number (TON) of 47 980 reported so far for this reaction.     

钌催化烯烃复分解反应的研究进展

综述了近年来在钌催化的烯烃复分解反应领域中的研究进展.着重介绍了该反应的各种基本类型的现状、应用和亟待解决的问题,并介绍了反应的机理以及催化剂的改进.     

Cascade Metathesis Reactions for the Synthesis of Taxane and Isotaxane Derivatives

Tricyclic isotaxane and taxane derivatives have been synthesized by a very efficient cascade ring‐closing dienyne metathesis (RCDEYM) reaction, which formed the A and B rings in one operation. When the alkyne is present at C13 (with no neighboring gem‐dimethyl group), the RCEDYM reaction leads to 14,15‐isotaxanes 16 a , b and 18 b with the gem‐dimethyl group on the A ring. If the alkyne is at the C11 position (and thus flanked by a gem‐dimethyl group), RCEDYM reaction only proceeds in the presence of a trisubstituted olefin at C13, which disfavors the competing diene ring‐closing metathesis reaction, to give the tricyclic core of Taxol 44 .     

Octasilsesquioxane Chemistry II. Hydrosilylation Reaction of Octa(hydrido)silsesquioxane with Unsaturated Substrates and Product Properties

The hydrosilylation reaction of octa(hydrido)silsesquioxane with ω‐halo‐1‐alkenes and other unsaturated substrates allows attachment of 8 long‐chain functionalized alkyls on the cubic Si₈O₁₂ skeleton. Pt/C and H₂PtCl₆ have been adopted as the catalysts, the yields being 74–98% for compounds 2–9 . For terminal alkenes, the hydrosilylation follows the anti‐Markonikov's rule. The morphological state of 2–9 ranges from viscous liquid to crystalline materials. The pyrolysis results indicate that 7 , a material of hard spherical core and soft flexible shell, may likely act as nanometer‐size ball bearings up to more than 400 °C. The X‐ray structure of 9 reveals that the molecule is required to possess a center of symmetry crystallographically. The linear arms on 9 , except for two of them, are virtually all‐trans in conformation, not counting the ω‐C‐Cl bond.     

Formal Total Synthesis of (−)‐Apicularen A by a Strategy Based on Ring‐Closing Metathesis and Transannular Cyclization

A formal synthesis of (?)‐apicularen A, a potent antitumor agent with unique biological properties, has been completed in a 15‐step sequence starting from a known, enantiomerically pure hydroxyepoxide, which was generated by using the Jacobsen hydrolytic‐kinetic‐resolution methodology. The 12‐membered macrocyclic lactone in the target was constructed by ring‐closing metathesis, and the trans‐tetrahydropyran ring system was created through the transannular etherification of a hydroxyalkene.     

Knoevenagel缩合反应研究的新进展

综述了近年来Knoevenagel缩合反应研究的新进展, 包括微波、超声波、固相合成、离子液体等新技术新试剂在该反应中的应用.     

A simple and efficient approach to 1,3-polyols: application to the synthesis of cryptocarya diacetate

A highly enantio- and stereoselective synthetic strategy for both syn- and anti-1,3-polyols has been developed. The sequence involves iterative Jacobsen's hydrolytic kinetic resolution (HKR), diastereoselective iodine-induced electrophilic cyclization, and ring-closing metathesis (RCM). This protocol has subsequently been utilized for the synthesis of cryptocarya diacetate, a natural product with broad range of biological activity.     

Conjugated BODIPY DYEmers by Metathesis Reactions

Boron dipyrrin (BODIPY) DYEmers bridged by conjugating ethynylene and ethenylene moieties can be prepared through metal‐promoted metathesis reactions. Alkyne metathesis was advantageous over alkene metathesis and Stille coupling for BODIPY substrates, but also showed specific restrictions with respect to steric encumbrance and regioselectivity. All derivatives with unhindered rotations along the bridges reside in a coplanar minimum conformation. For a hindered β‐ethenylene‐bridged DYEmer, the shifts in the ¹H NMR spectrum indicate a significant loss of coplanarity and conjugation. The electronic interactions of the BODIPY subchromophores, visualized by optical spectra and cyclic voltammograms, deviate significantly from those found for nonconjugated and excitonically coupled DYEmers. The observed properties can be rationalized in each case by the respective strength of conjugation through the α or β position, the degree of coplanarity, and conformational dynamics.     

烯胺酮与烯胺酯的交叉缩合反应及自缩合反应的区域选择性研究

烯胺酮与烯胺酯以(3C+3C)缩合反应形成多取代芳环化合物,具有区域选择性。用波谱和 X-射线衍射技术确定了产物的结构,讨论了反应机理。     

Enantioselective synthesis of tarchonanthuslactone via iterative hydrolytic kinetic resolution

A short and practical enantioselective synthesis of tarchonanthuslactone has been achieved in high diastereomeric excess using iterative Jacobsen’s hydrolytic kinetic resolution and ring closing metathesis as the key steps.     

Preparation and Optical Properties of Novel 3-Alkoxycarbonyl Aza- and Diazacoumarins

A series of 14 new 3-alkoxycarbonyl 6-aza-, 7-aza-, and 6,8-diaza-coumarins was prepared using various strategies involving either a Knoevenagel or a Pechmann condensation reaction. The coumarin nucleus displays different reactive functional groups allowing straightforward derivatization. The optical properties of the new azacoumarins were measured in methanol.     

Catalytic Isofunctional Reactions—Expanding the Repertoire of Shuttle and Metathesis Reactions

Transfer hydrogenation, alkene metathesis, and alkyne metathesis possess great value to the synthetic chemistry community. One of the key features of these processes is their reversibility, which can be attributed to the presence of the same number and type of functional groups in both the reactants and products, making these reactions isofunctional. These classic reactions have recently inspired the development of novel shuttle and metathesis reactions that offer great promise for synthetic chemistry. This Review describes and systematically categorizes both recent and older examples of shuttle and metathesis reactions other than transfer hydrogenation and alkene/alkyne metathesis.     

Studying and Suppressing Olefin Isomerization Side Reactions During ADMET Polymerizations

Olefin isomerization side reactions that occur during ADMET polymerizations were studied by preparing polyesters via ADMET and subsequently degrading these polyesters via transesterification with methanol. The resulting diesters, representing the repeating units of the previously prepared polyesters, were then analyzed by GC‐MS. This strategy allowed quantification of the amount of olefin isomerization that took place during ADMET polymerization with second generation ruthenium metathesis catalysts. In a second step, it was shown that the addition of benzoquinone to the polymerization mixture prevented the olefin isomerization. Therefore, second generation ruthenium metathesis catalysts may now be used for the preparation of well‐defined polymers via ADMET with very little isomerization, which was not possible before.