Towards Ideal Synthesis: Alkenylation of Aryl CH Bonds by a Fujiwara–Moritani Reaction

An overview of recent progress in the Fujiwara–Moritani reaction, which is the palladium‐catalyzed oxidative coupling of arenes with olefins to afford alkenyl arenes, is described. It is emphasized that regioselectivity on aryl ortho‐ or meta‐C?H activation could be controlled very well in the presence of Pd, Rh, or Ru catalysts with the assistance of various chelation groups on aromatic rings in this coupling reaction. Catalytic alkenylation of aryl C?H bonds from simple arenes is also discussed, especially from electron‐deficient arenes. These advanced protocols would not only make the Fujiwara–Moritani reaction more useful and applicable in organic synthesis but also light the way for the further development of the functionalization of normal C?H bonds.     

Oxidative amidation of aromatic aldehydes with amine hydrochloride salts catalyzed by silica‐coated magnetic carbon nanotubes (MagCNTs@SiO2)‐immobilized imine–Cu(I)

Mesoporous silica‐coated magnetic carbon nanotubes were prepared; their surface functionalization, followed by reaction with CuI, were carried out to develop a Cu‐grafted functionalized mesoporous material. This system is able to catalyze oxidative amidation of aromatic aldehydes with amine hydrochloride salts, generating amide derivatives in moderate to good yields. Magnetic properties of this catalyst led to easy separation as well as providing significant recyclability. Copyright © 2013 John Wiley & Sons, Ltd.     

Use of the Wilkinson Catalyst for the ortho‐CH Heteroarylation of Aromatic Amines: Facile Access to Highly Extended π‐Conjugated Heteroacenes for Organic Semiconductors

An unprecedented catalytic system composed of the Wilkinson catalyst [Rh(PPh₃)₃Cl] and CF₃COOH enabled the highly regioselective cross‐coupling of aromatic amines with a variety of heteroarenes through dual C? H bond cleavage. This protocol provided a facile and rapid route from readily available substrates to (2‐aminophenyl)heteroaryl compounds, which may be conveniently transformed into highly extended π‐conjugated heteroacenes. The experimental studies and calculations showed that thianaphtheno[3,2‐b]indoles have large HOMO–LUMO energy gaps and low‐lying HOMO levels, and could therefore potentially be high‐performance organic semiconductors. Herein we report the first use of a rhodium(I) catalyst for oxidative C? H/C? H coupling reactions. The current innovative catalyst system is much less expensive than [RhCp*Cl₂]₂/AgSbF₆ and could open the door for the application of this approach to other types of C? H activation processes.     

The Biocatalytic Repertoire of Natural Biaryl Formation

The catalytic and selective construction of carbon–carbon bonds for the generation of complex molecules is one of the most important tasks in organic chemistry. This was clearly highlighted by the 2010 Nobel Prize in Chemistry, which was awarded for the development of Pd‐catalyzed cross‐coupling reactions. The underlying concept of cross‐linking building blocks to generate molecular complexity can also be widely found in natural product biosynthesis. Impressive examples for such natural cross‐coupling reactions are biosynthetic processes for the assembly of biaryl moieties in natural products—highly efficient enzymatic reactions that often achieve synthetically yet unmatched selectivities. This Minireview highlights selected examples that showcase these fascinating biotransformations.     

Ruthenium‐Catalyzed Cascade CH Functionalization of Phenylacetophenones

Three orthogonal cascade C? H functionalization processes are described, based on ruthenium‐catalyzed C? H alkenylation. 1‐Indanones, indeno indenes, and indeno furanones were accessed through cascade pathways by using arylacetophenones as substrates under conditions of catalytic [{Ru(p‐cymene)Cl₂}₂] and stoichiometric Cu(OAc)₂. Each transformation uses C? H functionalization methods to form C? C bonds sequentially, with the indeno furanone synthesis featuring a C? O bond formation as the terminating step. This work demonstrates the power of ruthenium‐catalyzed alkenylation as a platform reaction to develop more complex transformations, with multiple C? H functionalization steps taking place in a single operation to access novel carbocyclic structures.     

Oxidative Dehydrogenation on Nanocarbon: Intrinsic Catalytic Activity and Structure–Function Relationships

Physical and chemical insights into the nature and quantity of the active sites and the intrinsic catalytic activity of nanocarbon materials in alkane oxidative dehydrogenation (ODH) reactions are reported using a novel in situ chemical titration process. A study on the structure–function relationship reveals that the active sites are identical both in nature and function on various nanocarbon catalysts. Additionally, the quantity of the active sites could be used as a metric to normalize the reaction rates, and thus to evaluate the intrinsic activity of nanocarbon catalysts. The morphology of the nanocarbon catalysts at the microscopic scale exhibits a minor influence on their intrinsic ODH catalytic activity. The number of active sites calculated from the titration process indicates the number of catalytic centers that are active (that is, working) under the reaction conditions.     

Enzymatic oxidative polymerization of para‐imine functionalized phenol catalyzed by horseradish peroxidase

Enzymatic oxidative polymerization of a new para‐imine functionalized phenol derivative, 4‐(4‐hydroxybenzylideneamino)benzoic acid (HBBA), using horseradish peroxidase enzyme and hydrogen peroxide oxidizer has been investigated in an equivolume mixture of an organic solvent (acetone, methanol, ethanol, dimethylformamide, 1,4‐dioxane, and tetrahydrofuran) and phosphate buffer (pH = 5.0, 6.0, 6.8, 7.0, 7.2, 8.0, and 9.0) at different temperatures under air for 24 h. The resulting oligomer, oligo(4‐(4‐hydroxybenzylideneamino)benzoic acid) [oligo(HBBA)], was characterized using ultraviolet–visible, Fourier transform infrared (FT‐IR), ¹H nuclear magnetic resonance (NMR), cyclic voltammetry, size exclusion chromatography, differential scanning calorimetry, and thermogravimetric analyses. Polymerization involved carbon dioxide and hydrogen elimination from the monomer, and terminal units of the oligomer structure consisted of phenolic hydroxyl (–OH) groups at the ends. The polymer is mainly composed of a mixture of phenylene and oxyphenylene units according to ¹H NMR and FT‐IR analyses. Effects of solvent system, temperature and buffer pH on the polymerization have been investigated in respect to the yield and molecular weight (M_n) of the product. The best condition in terms of the highest molecular weight (M_n = 3000 g/mol, DP ~ 15) was achieved in an equivolume mixture of 1,4‐dioxane/pH 5.0 phosphate buffer condition at 35°C. Electrochemical characterization of oligo(HBBA) was investigated at different scan rates. The resulting oligomer has also shown relatively high thermal stability according to thermogravimetric analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and Reactivity of New Functionalized Perfluoroalkylfluorophosphates

A new efficient synthesis of functionalized perfluoroalkyl fluorophosphates by oxidative addition of Me₂NCH₂F to the electron‐deficient phosphanes (C₂F₅)_nPF_3?n (n=0–3) is reported. The initially formed zwitterionic, hexacoordinated phosphates [(C₂F₅)_nF_5?nP(CH₂NMe₂?CH₂NMe₂)] are converted into the corresponding phosphonium salts [(Me₃PCH₂NMe₂]⁺[(C₂F₅)_nF_5?nP(CH₂NMe₂)]^? by treatment with PMe₃. In addition [(C₂F₅)₃F₂P(CH₂NMe₂?CH₂NMe₂)] can undergo a 1,3‐methyl shift from the internal to the terminal nitrogen—a structural characterization was achieved from the CF₃ analogue. Reaction of [(C₂F₅)₃F₂P(CH₂NMe?CH₂NMe₃)] and PMe₃ gave rise to the formation of the zwitterionic phosphonium phosphate [(C₂F₅)₃F₂P(CH₂NMe?CH₂PMe₃)], which was fully characterized by X‐ray diffraction analysis. Moreover, an efficient one‐pot synthesis of Cs⁺[(C₂F₅)₃F₂P(CH₂NMe₂)]^? was pursued. This salt turned out to be a useful nucleophile in several alkylation reactions.     

Total Synthesis of Indole Alkaloid Alsmaphorazine D

A concise total synthesis of rac‐alsmaphorazine D has been described for the first time. The efficient synthetic strategy features four key transformations: 1) a catalytic intramolecular oxidative cyclization for the δ‐lactamindole backbone; 2) an oxidative cyclic aminal formation for the hexahydropyrrolo[2,3‐b]pyrrole framework; 3) a transannular radical cyclization for the construction of the diazabicyclo[3.3.1]nonane structure; and 4) a one‐pot desilylation/double epimerization reaction that affirms the relative stereochemistry.     

酸处理对CuY催化剂孔结构及氧化羰基化性能的影响

对NaY分子筛(n_Si/n_Al=2.65)进行了草酸脱铝处理并作为载体采用液相离子交换法制备CuY催化剂,应用于常压甲醇氧化羰基化合成碳酸二甲酯(DMC)反应。NaY分子筛及其CuY催化剂通过N₂低温吸附-脱附、透射电子显微镜、X射线衍射、²⁹Si固体核磁共振、NH₃吸附程序升温脱附、吡啶吸附红外光谱、H₂程序升温还原、原子吸收等方法进行表征。研究结果表明,酸处理NaY分子筛后,骨架铝被脱除,导致骨架n_Si/n_Al比增加、相对结晶度降低并产生介孔,有利于产物分子的扩散,从而影响催化活性。采用4 h、2 mol·L^-1草酸处理NaY分子筛作为载体制备的CuY催化剂显示出较高的催化性能,DMC时空收率和甲醇转化率分别从103.6 mg·g^-1·h^-1和6.3%增加到184.9 mg·g^-1·h^-1和10.2%。产生的介孔能够促进催化剂中铜活性位的可接近性及反应物分子和产物分子的扩散。