Chemical Reactions of Coumarins and Furocoumarins on Thin-Layer Chromatoplates

Most of the reaction achieved in this work were conducted with coumarin and furocoumarin. The reactions were performed on inert thin-layer chromatoplates under controlled conditions and the products of the reactions were compared as usual with the expected substances on the same chromatogram. The reactions performed were: mineral acid hydrolysis, methylation, acetylation, benzoylation, nitration and Schiff's bases on silica gel chromatoplates.     

Flash chemistry: fast chemical synthesis by using microreactors

This concept article provides a brief outline of the concept of flash chemistry for carrying out extremely fast reactions in organic synthesis by using microreactors. Generation of highly reactive species is one of the key elements of flash chemistry. Another important element of flash chemistry is the control of extremely fast reactions to obtain the desired products selectively. Fast reactions are usually highly exothermic, and heat removal is an important factor in controlling such reactions. Heat transfer occurs very rapidly in microreactors by virtue of a large surface area per unit volume, making precise temperature control possible. Fast reactions often involve highly unstable intermediates, which decompose very quickly, making reaction control difficult. The residence time can be greatly reduced in microreactors, and this feature is quite effective in controlling such reactions. For extremely fast reactions, kinetics often cannot be used because of the lack of homogeneity of the reaction environment when they are conducted in conventional reactors such as flasks. Fast mixing using micromixers solves such problems. The concept of flash chemistry has been successfully applied to various organic reactions including a) highly exothermic reactions that are difficult to control in conventional reactors, b) reactions in which a reactive intermediate easily decomposes in conventional reactors, c) reactions in which undesired byproducts are produced in the subsequent reactions in conventional reactors, and d) reactions whose products easily decompose in conventional reactors. The concept of flash chemistry can be also applied to polymer synthesis. Cationic polymerization can be conducted with an excellent level of molecular-weight control and molecular-weight distribution control.     

Competing C-4 and C-5-Acyl Stabilization of Uronic Acid Glycosyl Cations

Uronic acids are carbohydrates carrying a terminal carboxylic acid and have a unique reactivity in stereoselective glycosylation reactions. Herein, the competing intramolecular stabilization of uronic acid cations by the C-5 carboxylic acid or the C-4 acetyl group was studied with infrared ion spectroscopy (IRIS). IRIS reveals that a mixture of bridged ions is formed, in which the mixture is driven towards the C-1,C-5 dioxolanium ion when the C-5,C-2-relationship is cis, and towards the formation of the C-1,C-4 dioxepanium ion when this relation is trans. Isomer-population analysis and interconversion barrier computations show that the two bridged structures are not in dynamic equilibrium and that their ratio parallels the density functional theory computed stability of the structures. These studies reveal how the intrinsic interplay of the different functional groups influences the formation of the different regioisomeric products.     

Efficient access to new chemical space through flow--construction of druglike macrocycles through copper-surface-catalyzed azide-alkyne cycloaddition reactions

A series of 12‐ to 22‐membered macrocycles, with druglike functionality and properties, have been generated by using a simple and efficient copper‐catalyzed azide–acetylene cycloaddition reaction, conducted in flow in high‐temperature copper tubing, under environmentally friendly conditions. The triazole‐containing macrocycles have been generated in up to 90 % yield in a 5 min reaction, without resorting to the high‐dilution conditions typical of macrocyclization reactions. This approach represents a very efficient method for constructing this important class of molecules, in terms of yield, concentration, and environmental considerations.     

Ion structure determinations and ion—molecule reactions by double quadrupole mass spectrometry

The QQ mass spectrometer is shown to be applicable to ion structure determination via collision-induced dissociations of mass-selected ions. The instrument can be scanned so as to record the products of dissociation as well as those of ion—molecule association reactions. The dissociations correspond to those observed at high kinetic energy in mass-analyzed ion kinetic energy spectrometers and the association reactions show parallels with reactions seen in ion cyclotron resonance spectroscopy and in high-pressure mass spectrometry     

Solvent- and metal-free selective oxidation of thiols to disulfides using I2/DMSO catalytic system

We describe herein a simple, fast and inexpensive protocol for the oxidative coupling of thiols employing a stoichiometric amount of DMSO and iodine as the catalyst. Various aromatic disulfides were obtained in good to excellent yields in short reaction times at room temperature, while aliphatic disulfides were achieved in good yields when the reactions were conducted under microwave irradiation.     

Scope and mechanistic insights into the use of tetradecyl(trihexyl)phosphonium bistriflimide: a remarkably selective ionic liquid solvent for substitution reactions

A survey of substitution reactions conducted in a phosphonium bistriflimide ionic liquid is presented. The results demonstrate high selectivity favoring substitution over typically competitive elimination and solvolytic processes even when challenging secondary and tertiary electrophiles are employed. The first reports of Kornblum substitution reactions in an ionic liquid are described that proceed with very high chemoselectivity in favor of nitro over nitroso products and elimination side products. The structure-reactivity study indicates that these reactions proceed through a narrow spectrum of pathways ranging from straight S(N)2 to a preassociation pathway along a saddle point that approaches the S(N)1 limit. The barrier to the formation of dissociated carbocations is attributed to the structural features of this ionic liquid that favor intervention of the associated nucleophile over dissociation, also preventing cross over to E1 processes. The lack of any basic entity in the phosphonium bistriflimide ionic liquid appears to prevent any potential base-mediated elimination reactions, which makes this a highly selective medium for use in general substitution reactions.     

Studies on the stereochemistry of addition reactions of cyclohexanones : A dichotomy in substituent effect depending on reaction conditions

The stereochemistry of addition reactions of 4-t-Bu, 4-OMe and 4-C1 cyclohexanones, determined under seven different reaction conditions is described. A dichotomy in the substituent influence on stereochemistry is outlined and discussed suggesting that it parallels the changes in reaction mechanism.     

trans‐Symmetric Dynamic Covalent Systems: Connected Transamination and Transimination Reactions

The development of chemical transaminations as a new type of dynamic covalent reaction is described. The key 1,3‐proton shift is under complete catalytic control and can be conducted orthogonally to, or simultaneous with, transimination in the presence of an amine to rapidly yield two‐dimensional dynamic systems with a high degree of complexity evolution. The transamination–transimination systems are proven to be fully reversible, stable over several days, compatible with a range of functional groups, and highly tunable. Kinetic studies show transamination to be the rate‐limiting reaction in the network. Furthermore, it was discovered that readily available quinuclidine is a highly potent catalyst for aldimine transaminations. This study demonstrates how connected dynamic reactions give rise to significantly larger systems than the unconnected counterparts, and shows how reversible isomerizations can be utilized as an effective diversity‐generating element.     

Heuristic Chemistry—Elimination Reactions

Besides additions and substitutions, elimination reactions play a fundamental role in organic synthesis. However, conceptual reviews of known 1,x‐elimination patterns that go beyond the typical olefin‐forming 1,2‐eliminations are scarce. To develop a broader understanding of elimination reactions, we follow a heuristic approach and deduce recurrent reaction patterns from traditional and specific elimination reactions. Our work demonstrates that 1,x‐elimination reactions and their outcomes can be easily rationalized by defined mnemonic categories.     

点击化学及其应用

点击化学反应选用易得原料，通过可靠、高效化学反应快速合成大量新化合物，且反应条件温和、产物收率高和不需要专门的分离提纯。本文介绍了点击化学（click chemistry）的一些基本概念，综述了点击化学作为一种新的合成方法在药物中的先导化合物库、糖类化合物、天然化合物、生物大分子和高分子中聚合物上的应用，并对其发展前景进行了展望。     

Dynamic Covalent Chemistry of Nucleophilic Substitution Component Exchange of Quaternary Ammonium Salts

Dynamic covalent libraries (DCLs) of quaternary ammonium cations were set up by reversible nucleophilic substitution (S_N2′ and S_N2) exchange reactions of ammonium salts and tertiary amines. The reactions were conducted at 60 °C to generate thermodynamically and kinetically controlled mixtures of quaternary ammonium compounds and tertiary amines, and were accelerated by using iodide as a nucleophilic catalyst. Microwave irradiation was used to assist the exchange reaction between the pyridinium salts and pyridine derivatives. Finally, experiments towards the generation of dynamic ionic liquids were performed. The results of this study pave the way for the extension of dynamic combinatorial chemistry to nucleophilic substitution reactions.     

The Enzymology of Organic Transformations: A Survey of Name Reactions in Biological Systems

Chemical reactions that are named in honor of their true, or at least perceived, discoverers are known as “name reactions”. This Review is a collection of biological representatives of named chemical reactions. Emphasis is placed on reaction types and catalytic mechanisms that showcase both the chemical diversity in natural product biosynthesis as well as the parallels with synthetic organic chemistry. An attempt has been made, whenever possible, to describe the enzymatic mechanisms of catalysis within the context of their synthetic counterparts and to discuss the mechanistic hypotheses for those reactions that are currently active areas of investigation. This Review has been categorized by reaction type, for example condensation, nucleophilic addition, reduction and oxidation, substitution, carboxylation, radical‐mediated, and rearrangements, which are subdivided by name reactions.     

Heuristic chemistry--addition reactions

Organic chemistry is often considered a difficult subject requiring great effort to achieve expert status. Only once this level has been reached, judging, deciding, and recalling chemical information will be fast and guided by heuristic strategies. These principles, used intuitively, improve the efficiency and speed of problem-solving and decision-making procedures. Establishing these strategies in teaching and learning chemistry should significantly help students acquire well-structured procedural knowledge early in their education. In an attempt to improve conceptual thinking in teaching organic chemistry, in this contribution we develop a heuristic view of addition reactions and propose a new way of perceiving this class of organic reactions.     

Rolf Huisgen's Classic Studies of Cyclic Triene Diels–Alder Reactions Elaborated by Modern Computational Analysis

Rolf Huisgen explored the Diels–Alder reactions of 1,3,5-cycloheptatriene (CHT) and cyclooctatetraene (COT) with the dienophiles maleic anhydride and 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) to determine the kinetics and mechanisms of various electrocyclizations and Diels–Alder reactions. These reactions have been examined with density functional theory. Modern computational chemistry has provided information not previously available by experiment. Transition states for all the reactions have been identified, and their Gibbs energies are used to explain the experimental reactivities. Zwitterionic intermediates were not found in the [4+2] cycloadditions of both CHT or COT with PTAD and are thus not involved in these reactions. [2+2+2] cycloadditions, as an alternative path to the Diels–Alder products, are highly disfavored. Rapid double nitrogen inversion was found for the cycloaddition products with PTAD.     

Amination with Pd-NHC complexes: rate and computational studies on the effects of the oxidative addition partner

Pd-PEPPSI-IPent, a recently-developed N-heterocyclic carbene (NHC) complex, has been evaluated in amination reactions with secondary amines and it has shown superb reactivity under the most mildly basic reaction conditions. Rate and computational studies were conducted to provide insight into the mechanism of the transformation. The IPent catalyst coordinates to the amine much more strongly than the IPr variant, thus favouring deprotonation with comparatively weak bases. Indeed the reaction is first order in base and only slightly more than zeroth order in amine.     

Some Advances in the Inorganic Chemistry of Bromine

Recent advances in the chemistry of bromine and its inorganic compounds are covered under the headings of technology, properties and reactions, liquid bromine as an inorganic solvent, analysis, and new or newly studied compounds. Much of what is new is bromine chemistry is characteristic also of what is new in inorganic chemistry as a whole. That is, more detailed information about compounds and reactions is becoming available from the application of new instrumental and theoretical techniques.     

Growth Processes due to Reactions in Swellable Cellular Matrixes

In matrix reactions in swellable cellular matrixes, the solids formed are oriented in space and arranged in the form of cells in strong three-dimensional growth processes. Open-cell, flexible, elastic polyurethanes have a particularly good matrix action. The principle is of general validity, and can be realized with a wide variety of matrixes and reaction types. The dimensional changes, which are always symmetrical, are largely determined by the chemical constitution of the matrix, segment structure, degree of crosslinking, and solvation and hydration behavior. One-component reactions having high rates give sigmoid growth curves and exhibit parallels with growth curves of plant cell walls containing cellulose.     

Synthesis of Polycyclic Aminocyclobutane Systems by the Rearrangement of N‐(ortho‐Vinylphenyl) 2‐Azabicyclo[3.1.0]hexane Derivatives

The acid‐catalysed thermal rearrangements of a family of N‐aryl 2‐azabicyclo[3.1.0]hexanes is described. These substrates, designed in such a way that the aromatic system is conjugated with an alkene group located at the ortho position relative to the nitrogen atom, have been prepared by using an intramolecular Kulinkovich–de Meijere reaction. The rearrangements can then be conducted either under standard thermal conditions or with microwave activation. Depending on the conditions applied and the substitution pattern, dihydroquinoline or polycyclic aminocyclobutane derivatives can be obtained. A mechanistic discussion is provided, with the proposition of the initial protonation of the aminocyclopropane moiety to give an iminium intermediate. By analogy with related intermolecular reactions, the involvement of electrocyclic reactions among the series of elementary steps that follow is put forward.     

Solar Photooxygenations for the Manufacturing of Fine Chemicals—Technologies and Applications

Photooxygenation reactions involving singlet oxygen (¹O₂) are utilized industrially as a mild and sustainable access to oxygenated products. Due to the usage of organic dyes as photosensitizers, these transformations can be successfully conducted using natural sunlight. Modern solar chemical reactors enable outdoor operations on the demonstration (multigram) to technical (multikilogram) scales and have subsequently been employed for the manufacturing of fine chemicals such as fragrances or biologically active compounds. This review will highlight examples of solar photooxygenations for the manufacturing of industrially relevant target compounds and will discuss current challenges and opportunities of this sustainable methodology.