Catalytic Methylation of C?H Bonds Using CO2 and H2

Formation of C C bonds from CO₂ is a much sought after reaction in organic synthesis. To date, other than C H carboxylations using stoichiometric amounts of metals, base, or organometallic reagents, little is known about C C bond formation. In fact, to the best of our knowledge no catalytic methylation of C H bonds using CO₂ and H₂ has been reported. Described herein is the combination of CO₂ and H₂ for efficient methylation of carbon nucleophiles such as indoles, pyrroles, and electron‐rich arenes. Comparison experiments which employ paraformaldehyde show similar reactivity for the CO₂/H₂ system.     

Enantiospecific C?H Activation Using Ruthenium Nanocatalysts

The activation of C H bonds has revolutionized modern synthetic chemistry. However, no general strategy for enantiospecific C H activation has been developed to date. We herein report an enantiospecific C H activation reaction followed by deuterium incorporation at stereogenic centers. Mechanistic studies suggest that the selectivity for the α‐position of the directing heteroatom results from a four‐membered dimetallacycle as the key intermediate. This work paves the way to novel molecular chemistry on nanoparticles.     

Oxindole Synthesis by Direct Coupling of C?H and C?H Centers

An sp ² /sp ³ get‐together : A novel and efficient method can be used to synthesize 3,3‐disubstitued oxindoles by the direct intramolecular oxidative coupling of an aryl C? H and a C? H center (see scheme; DMF=N,N‐dimethylformamide).

     

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.     

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.     

Visible light-mediated photocatalyzed synthesis of oxazole via intermolecular C?N and C?O bond formation

An efficient visible light-mediated, eosin Y-catalyzed synthesis of oxazole has been developed from benzil with primary amines, that providing a straightforward, green, and environmentally benign access to a wide variety of substituted oxazole-2-amines under mild reaction conditions.     

Kinetics and modeling of the H2?O2?NOx system

The addition of NO (0 to 400ppm) to mixtures of H₂ (ca. 1%) and O₂ (0.7 to 22%) has been studied over the temperature range 700 to 825 K, in a flow reactor at atmospheric pressure. The overall effect of NO is to promote the oxidation of H₂ but high concentrations of O₂ actually inhibit the NO-promoted oxidation of H₂. A detailed kinetic mechanism has been constructed and found to describe the experimental observations. The promotion of the oxidation of H₂ arises through the catalytic cycle The ability of R.34 to reactivate chains normally terminated by the formation of HO₂ is a key feature of this system. The predictions are highly sensitive to the rate of the reaction R.5 and the rate constants for this reaction is the only adjustable parameter required in the model. The value of k_5,N2 found to describe all the results has an absolute uncertainty <35%. The uncertainty relative to other important rate constants in the H₂? O₂ system is less than 10%. © 1995 John Wiley & Sons, Inc.     

Highly Efficient C?H Hydroxylation of Carbonyl Compounds with Oxygen under Mild Conditions

A transition‐metal‐free Cs₂CO₃‐catalyzed α‐hydroxylation of carbonyl compounds with O₂ as the oxygen source is described. This reaction provides an efficient approach to tertiary α‐hydroxycarbonyl compounds, which are highly valued chemicals and widely used in the chemical and pharmaceutical industry. The simple conditions and the use of molecular oxygen as both the oxidant and the oxygen source make this protocol very environmentally friendly and practical. This transformation is highly efficient and highly selective for tertiary C(sp³) H bond cleavage.     

Nitrene Insertion into C?C and C?H Bonds of Diamide Diimine Ligands Ligated to Chromium and Iron

The impact of redox non‐innocence (RNI) on chemical reactivity is a forefront theme in coordination chemistry. A diamide diimine ligand, [{‐CHN(1,2‐C₆H₄)NH(2,6‐iPr₂C₆H₃)}₂]ⁿ (n=0 to −4), (dadi)ⁿ, chelates Cr and Fe to give [(dadi)M] ([ 1 Cr(thf)] and [ 1 Fe]). Calculations show [ 1 Cr(thf)] (and [ 1 Cr]) to have a d⁴ Cr configuration antiferromagnetically coupled to (dadi)²⁻*, and [ 1 Fe] to be S=2. Treatment with RN₃ provides products where RN is formally inserted into the C C bond of the diimine or into a C H bond of the diimine. Calculations on the process support a mechanism in which a transient imide (imidyl) aziridinates the diimine, which subsequently ring opens.     

Synthesis and properties of fluorinated benzotriazole-based donor-acceptor-type conjugated polymers via Pd-catalyzed direct C?H/C?H coupling polymerization

Fluorine substituted benzotriazole (BTz) units have shown great potential in improving various conjugated polymers (CPs)-based optoelectronic devices' performance. Thus, it is highly expected for the establishment of simple, efficient, and inexpensive accesses to such polymers. In this paper, Pd-catalyzed direct C H/C H coupling polymerization is first employed for the synthesis of 5,6-difluorobenzotriazole containing π-CPs, which fully avoids prefunctionalization of monomers. Under the optimized conditions, a series of donor-acceptor-type π-CPs with excellent regio-regularity are facilely obtained via the direct C H/C H coupling reaction of 5,6-difluoro-2-(2-hexyldecyl)-2H-BTz with different thiophene analogs. The chemical structure of the as-synthesized polymers are confirmed by NMR technique including ¹H NMR, ¹⁹F NMR, and the edited heteronuclear singular quantum correlation and heteronuclear multiple bond correlation spectra as well as comparative study on the same polymers obtained via Stille coupling and direct (hetero)arylation polymerization. Further, their optical properties, electrochemical properties, and thermal stabilities are also carefully explored by UV–Vis absorption spectra, cyclic voltammograms as well as thermogravimetric analysis, respectively. On the basis of density functional theory (DFT) simulation, the effect of alkyl substituents attached to thiophene units on the reactivity and optical performance of the resultant polymers is explained. Our protocol exhibits remarkable advantages in synthetic simplicity, atom-economy, high efficiency, and excellent regioselectivity of cross-coupling, providing an alternative synthetic strategy for high-performance optoelectronic materials.