C?C Fragmentation: Origins and Recent Applications

It has been 60 years since Eschenmoser and Frey disclosed the archetypal C? C fragmentation reaction. New fragmentations and several variants of the original quickly followed. Many of these variations, which include the Beckmann, Grob, Wharton, Marshall, and Eschenmoser–Tanabe fragmentations, have been reviewed over the intervening years. A close examination of the origins of fragmentation has not been described. Recently, useful new methods have flourished, particularly fragmentations that give alkynes and allenes, and such reactions have been applied to a range of complex motifs and natural products. This Review traces the origins of fragmentation reactions and provides a summary of the methods, applications, and new insights of heterolytic C? C fragmentation reactions advanced over the last 20 years.     

Gold for C?C Coupling Reactions: A Swiss‐Army‐Knife Catalyst?

For organic chemists, the construction of C C bonds is the most essential aspect of the assembly of molecules. Transition‐metal‐catalyzed coupling reactions have evolved as one of the key tools for this task. Lately, gold has also emerged as a catalyst for this kind of transformation. Gold, with its special properties as a mild carbophilic π Lewis acid, its ability to insert into C H bonds, and, as discovered recently, its ability to undergo redox transformations, offers the opportunity to apply all this potent proficiency for the construction of compounds in an efficient and economical way. This Minireview critically presents the C C coupling reactions enabled by gold catalysts to encourage further research activities in this promising area of oxidation/reduction gold catalysts.     

Studies on the Synthesis and Characterization of Pd?TiO2?SiO2 Nanocomposite for Electroanalytical Applications

A nanocomposite of Pd? TiO₂? SiO₂ is developed through a sol‐gel process from the reaction products of titanium isopropoxide followed by mixing the same with palladium linked 3‐glycidoxypropyltrimethoxysilane. The reaction product is sonicated and calcinated to obtain the nanocomposite of Pd? TiO₂? SiO₂. The calcination at 600 °C yielded an amorphous structure whereas at 900 °C it resulted into a nanocrystalline structure. The nanocomposite of palladium was further characterized by TEM, XRD, IR and EDS. The material acts as an efficient electrocatalyst. Electrocatalysis of ascorbic acid is observed at 0.1 V vs. Ag/AgCl, shows linearity between 1 µM and 1 mM in 0.1 M phosphate buffer (pH 7.0).     

Silver-Catalysed Enantioselective Addition of O?H and N?H Bonds to Allenes: A New Model for Stereoselectivity Based on Noncovalent Interactions

The ability of silver complexes to catalyse the enantioselective addition of O H and N H bonds to allenes is demonstrated for the first time by using optically active anionic ligands that were derived from oxophosphorus(V) acids as the sources of chirality. The intramolecular addition of acids, alcohols, and amines to allenes can be achieved with up to 73 % ee. The exploitation of a C H anomeric effect allowed the absolute configuration of a sample of 2-substituted tetrahydrofuran of low ee to be unambiguously assigned by comparison of the chiroptical ORD and VCD measurements with calculated spectra. In the second part of the work, the origin of the stereoselectivity was probed by DFT free-energy calculations of the transition states. A new model of enantiomeric differentiation was developed that was based on noncovalent interactions. This model allowed us to identify the source of stereoselectivity as weak attractive interactions; such dispersive forces are often overlooked in asymmetric catalysis. A new computational approach was developed that represents these interactions as colour-coded isosurfaces that are characterised by the reduced density-gradient profile.     

Ionic Liquids: New Perspectives for Inorganic Synthesis?

Ionic liquids are credited with a number of unusual properties. These include a low vapor pressure, a wide liquid‐phase range, weakly coordinating properties, and a high thermal/chemical stability. These properties are certainly of great interest for inorganic synthesis and the creation of novel inorganic compounds. On the other hand, the synthesis repertoire for preparing inorganic compounds has always been broad, ranging from syntheses in solutions and melts to solid‐state reactions, and from crystal growth in the gas phase to high‐pressure syntheses. What new aspects can ionic liquids then add to the synthesis of inorganic compounds? This Minireview uses some early examples to show that the use of ionic liquids indeed provides access to unusual inorganic compounds.     

Elevating the Triplet Energy Levels of Dibenzofuran‐Based Ambipolar Phosphine Oxide Hosts for Ultralow‐Voltage‐Driven Efficient Blue Electrophosphorescence: From D?A to D?π?A Systems

A series of donor (D)–π–acceptor (A)‐type phosphine‐oxide hosts ( DBF _x POPhCz _n ), which were composed of phenylcarbazole, dibenzofuran ( DBF ), and diphenylphosphine‐oxide (DPPO) moieties, were designed and synthesized. Phenyl π‐spacer groups were inserted between the carbazolyl and DBF groups, which effectively weakened the charge transfer and triplet‐excited‐state extension. As the result, the first triplet energy levels (T₁) of DBF _x POPhCz _n are elevated to about 3.0 eV, 0.1 eV higher than their D? A‐type analogues. Nevertheless, the electrochemical analysis and DFT calculations demonstrated the ambipolar characteristics of DBF _x POPhCz _n . The phenyl π spacers hardly influenced the frontier molecular orbital (FMO) energy levels and the carrier‐transporting ability of the materials. Therefore, these D? π? A systems are endowed with higher T₁ states, as well as comparable electrical properties to D? A systems. Phosphorescent blue‐light‐emitting diodes (PHOLEDs) that were based on DBF _x POPhCz _n not only inherited the ultralow driving voltages (2.4 V for onset, about 2.8 V at 200 cd m^?2, and <3.4 V at 1000 cd m^?2) but also had much‐improved efficiencies, including about 26 cd A^?1 for current efficiency, 30 Lm W^?1 for power efficiency, and 13 % for external quantum efficiency, which were more than twice the values of devices that are based on conventional unipolar host materials. This performance makes DBFDPOPhCz _n among the best hosts for ultralow‐voltage‐driven blue PHOLEDs reported so far.     

Amide‐Directed Tandem C?C/C?N Bond Formation through C?H Activation

The transformation of C? H bonds into other chemical bonds is of great significance in synthetic chemistry. C? H bond‐activation processes provide a straightforward and atom‐economic strategy for the construction of complex structures; as such, they have attracted widespread interest over the past decade. As a prevalent directing group in the field of C? H activation, the amide group not only offers excellent regiodirecting ability, but is also a potential C? N bond precursor. As a consequence, a variety of nitrogen‐containing heterocycles have been obtained by using these reactions. This Focus Review addresses the recent research into the amide‐directed tandem C? C/C? N bond‐formation process through C? H activation. The large body of research in this field over the past three years has established it as one of the most‐important topics in organic chemistry.     

A New Dynamic Covalent Bond of Se?N: Towards Controlled Self‐Assembly and Disassembly

A new kind of Se? N dynamic covalent bond has been found that can form between the Se atom of a phenylselenyl halogen species and the N atom of a pyridine derivative, such as polystyrene‐b‐poly(4‐vinylpyridine). This Se? N dynamic covalent bond can be reversibly and rapidly formed or cleaved under acidic or basic conditions, respectively. Furthermore, the bond can be dynamically cleaved by heating or treatment with stronger electron‐donating pyridine derivatives. The multiple responses of Se? N bond to external stimuli has enriched the existing family of dynamic covalent bonds. It can be used for controlled and reversible self‐assembly and disassembly, which may find potential applications in a number of areas, including self‐healing materials and responsive assemblies.     

Sulfoximid und Sulfoximidium-Salze – Strukturen und H?Brückenbindungen

Sulfoximide and Sulfoximidium Salts – Structures and Hydrogen Bonding In the solid state dimethylsulfoximide ( 1 ) (orthorhombic; space group Pbca; a = 577.8, b = 931.2 and c = 1645.6 pm) makes intermolecular N? H ? N hydrogen bonds. The hydrogen halide salts (CH₃)₂S(O)NH₂⁺Hal^? (( 2 ), Hal^??Cl^?; ( 4 ), Hal^??Br^?) reacts with metal halides to yield (CH₃)₂S(O)NH₂⁺MHal with the complex anions (( 5 ), MHal?SbCl₄^?; ( 6 ), MHal?SbCl₅^2?; ( 7 ), MHal?SbCl₆^?; ( 8 ), MHal?SbBr₅^2?; ( 9 ), MHal?AlCl₄^?). 2 crystallizes from ethanol (96%) as [(CH₃)₂S(O)NH₂⁺Cl^?]₂ · H₂O ( 3 ). The structures of 3 (monoclinic; space group P2₁/c; a = 917.0, b = 1344.7, c = 1080.8 pm and β = 103.8°; Z = 10), 4 (orthorhombic; space group Pbcn; a = 1028.9, b = 1132.6, c = 1074.1 pm; Z = 8) and 6 (monoclinic; space group C2/c; a = 2041.1, b = 1101.4, c = 3365.6 pm and β = 153.8°; Z = 8) are determined by X-ray analysis. In 6 Sb is coordinated in a distorted octahedra by 6 Cl in three short (mean 245,5 pm; SbCl₃) and three long distances (291 to 299 pm; Cl^?). Two of the chloride ions connect the Sb atoms to infinite Sb …? Cl …? Sb chains. Except for 7 and 9 there are bridges between the NH₂ groups and the halide ions. The NH valence vibrations are discussed in view of hydrogen bonding.     

Catalytic C?C,C?N,and C?O Ullmann‐Type Coupling Reactions

Copper‐catalyzed Ullmann condensations are key reactions for the formation of carbon–heteroatom and carbon–carbon bonds in organic synthesis. These reactions can lead to structural moieties that are prevalent in building blocks of active molecules in the life sciences and in many material precursors. An increasing number of publications have appeared concerning Ullmann‐type intermolecular reactions for the coupling of aryl and vinyl halides with N, O, and C nucleophiles, and this Minireview highlights recent and major developments in this topic since 2004.     

The ?NH?(C)?Br functionality of heteroaromatic compounds as a synthon for fused dihydrooxazoles

Fused dihydrooxazoles are produced by the reaction of 8‐bromoteophylline (1), 6‐bromo‐2‐pyridone (7), or 2‐bromobenzimidazole (11) with an N‐substituted N‐(2,3‐epoxypropyl)amine. The product derived from 1 undergoes rearrangement to a fused dihydrooxazine while the fused dihydrooxazoles derived from 7 and 11 are stable. J. Heterocyclic Chem., (2011).