Insertion Of Carbon Atoms Research Articles

Skeletal Editing through Single-Atom Insertion and Transmutation: An Insight into a New Era of Synthetic Organic Chemistry

AbstractConsidering the importance of heterocycles, significantly represented in medicinal chemistry and drug development, the single-atom insertion technique and transmutation strategy provide productive approaches towards complicated molecular structures through heterocycle diversification. It shows a potentially powerful approach for modifying complex substrates concisely and chemospecifically. Although skeletal editing applies to cyclic and acyclic compounds, this review focuses on the diversification of carbo- and heterocyclic compounds for synthesizing various medicinally important molecules via the single-atom insertion technique. The classification system is based on recent and critical historical methods of single-atom insertion as applied to the transmutation of aromatic rings.1 Introduction2 Skeletal Editing through Carbon-Atom Insertion2.1 Skeletal Editing of Indoles and Pyrroles Derivatives: Carbon-Atom Insertion into a C=C Bond2.2 Skeletal Editing of Pyrazole and Indazole Derivatives: Carbon-Atom Insertion into an N–N Bond2.3 Skeletal Editing of Pyrazole and Indazole Derivatives: Insertion of CF3 Group into Heteroarenes2.4 Skeletal Editing of Imidazole Derivatives: Carbon-Atom Insertion into C–N Bond2.5 Skeletal Editing through Atom-to-Atom Transmutation3 Skeletal Editing through N-Atom Insertion3.1 Nitrogen-Atom Insertion into Carbocycles3.2 Nitrogen-Atom Insertion into Heterocycles3.3 Carbon to Nitrogen Transmutation3.3 Molecular Editing through Isotopic Transmutation4 Conclusion

Silver-Catalyzed Single-Carbon Insertion of Indoles with Acetophenone N-Triftosylhydrazones.

Here, we report a silver carbene-enabled single-carbon insertion reaction of indoles via a one-pot, two-step sequence to deliver a dearomative quaternary center quinoline scaffold in a modular fashion. Specifically, we used N-triftosylhydrazones as masked donor-donor carbene precursors that facilitate the insertion of carbon atoms bearing various functional groups to the library of functionalized quinoline. Experimental and DFT evidence support the transient presence of a cyclopropane species and removal of protecting groups.

Controllable Skeletal and Peripheral Editing of Pyrroles with Vinylcarbenes.

The skeletal editing of azaarenes through insertion, deletion, or swapping of single atoms has recently gained considerable momentum in chemical synthesis. Here, we describe a practical skeletal editing strategy using vinylcarbenes in situ generated from trifluoromethyl vinyl N-triftosylhydrazones, leading to the first dearomative skeletal editing of pyrroles through carbon-atom insertion. Furthermore, depending on the used catalyst and substrate, three types of peripheral editing reactions of pyrroles are also disclosed: α- or γ-selective C-H insertion, and [3+2] cycloaddition. These controllable molecular editing reactions provide a powerful platform for accessing medicinally relevant CF3-containing N-heterocyclic frameworks, such as 2,5-dihydropyridines, piperidines, azabicyclo[3.3.0]octadienes, and allylated pyrroles from readily available pyrroles. Mechanistic insights from experiments and density functional theory (DFT) calculations shed light on the origin of substrate- or catalyst-controlled chemo- and regioselectivity as well as the reaction mechanism.

Ring expansion of indene by photoredox-enabled functionalized carbon-atom insertion

Ring expansion of indene by photoredox-enabled functionalized carbon-atom insertion

Skeletal Editing through Molecular Recombination of 2H-Indazoles to Azo-Linked-Quinazolinones.

A new protocol by the combinatory use of two equivalent of indazoles starting material with one being the carbon source via its C3-reactivity and the other, the coupling partner has been developed for the selectfluor-mediated single atom skeletal editing of 2H-indazoles. The azo-linked-2,3-disubstituted quinazolin-4-one derivatives were obtained through a carbon atom insertion between the two nitrogens of the indazole ring and simultaneous oxidation at C3 position of both indazole moieties. Mechanistic investigations reveal that the amidic carbonyl oxygen of the product is derived from water and the reaction proceeds through in-situ generated N-centred indazolone radical intermediate.

Progress in the Synthesis and Catalytic Properties of Molybdenum Carbide Materials

Molybdenum carbide is a new type of material with excellent physical and chemical properties due to the intercalation structure formed by the insertion of carbon atoms, which not only has the properties of a functional material, but also has excellent catalytic properties in the fields of hydrogenation and hydrogen production reactions. This paper reviews the properties and synthesis methods of molybdenum carbide, systematically introduces the advantages and disadvantages of different methods, and finally summarizes the applications of molybdenum carbide in catalytic hydrogenation, catalytic hydrogen production and photoelectric catalysis, and analyzes the current challenges and future directions of molybdenum carbide materials.

In Situ Investigations on Structural Evolutions during the Facile Synthesis of Cubic α-MoC1-x Catalysts.

Cubic α-phase molybdenum carbides (α-MoC1-x) exhibit great potential in hydrogen production at low temperatures due to their excellent activity in water dissociation. However, the design strategies of α-MoC1-x are severely restricted by the harsh synthesis conditions, which involve multistep ammonification and carburization or the utilization of a significant amount of noble metals. Herein, high-purity α-MoC1-x synthesis in a one-step carburization process was achieved with the assistance of a trace amount of Rh (0.02%). The structural evolution of Mo species during phase transition was monitored via qualitative and quantitative analysis by in situ X-ray diffraction (XRD) and in situ X-ray absorption spectroscopy (XAS), respectively. Environmental transmission electron microscopy (ETEM) was used to follow the visual changes. We reveal that the reduction of monoclinic MoO3 to cubic oxygen-deficient Mo oxide (MoOx) at low temperatures owing to the promoted H2 activation on Rh sites is vital to the following carbon atom insertion and transformation to α-MoC1-x, making the carburization follow the topological route. The systematic analysis of the relationship between the reduction behavior and the structural evolution supplies a feasible strategy for the α-MoC1-x synthesis, and in situ characterizations shed light on controlling the phase transformation during carburization.

Unified Access to Pyrimidines and Quinazolines Enabled by N-N Cleaving Carbon Atom Insertion.

Given the ubiquity of heterocycles in biologically active molecules, transformations with the capacity to modify such molecular skeletons with modularity remain highly desirable. Ring expansions that enable interconversion of privileged heterocyclic motifs are especially interesting in this regard. As such, the known mechanisms for ring expansion and contraction determine the classes of heterocycle amenable to skeletal editing. Herein, we report a reaction that selectively cleaves the N-N bond of pyrazole and indazole cores to afford pyrimidines and quinazolines, respectively. This chlorodiazirine-mediated reaction provides a unified route to a related pair of heterocycles that are otherwise typically prepared by divergent approaches. Mechanistic experiments and DFT calculations support a pathway involving pyrazolium ylide fragmentation followed by cyclization of the ring-opened diazahexatriene intermediate to yield the new diazine core. Beyond enabling access to valuable heteroarenes from easily prepared starting materials, we demonstrate the synthetic utility of skeletal editing in the synthesis of a Rosuvastatin analog as well as in an aryl vector-adjusting direct scaffold hop.

A crossed molecular beams and computational study on the unusual reactivity of banana bonds of cyclopropane (c-C3H6; ) through insertion by ground state carbon atoms (C(3Pj)).

The mechanism and chemical dynamics of the reaction of ground electronic state atomic carbon C(3Pj) with cyclopropane c-C3H6 have been explored by combining crossed molecular beams experiments with electronic structure calculations of the pertinent triplet C4H6 potential energy surface and statistical computations of product branching ratios under single-collision conditions. The experimental findings suggest that the reaction proceeds via indirect scattering dynamics through triplet C4H6 reaction intermediate(s) leading to C4H5 product(s) plus atomic hydrogen via a tight exit transition state, with the overall reaction exoergicity evaluated as 231 ± 52 kJ mol-1. The calculations indicate that C(3Pj) can easily insert into one of the three equivalent C-C 'banana' bonds of cyclopropane overcoming a low barrier of only 2 kJ mol-1 following the formation of a van der Waals reactant complex stabilized by 15 kJ mol-1. The carbon atom insertion into one of the six C-H bonds is also feasible via a slightly higher barrier of 5 kJ mol-1. These results highlight an unusual reactivity of cyclopropane's banana C-C bonds, which behave more like unsaturated C-C bonds with a π-character than saturated σ C-C bonds, which are known to be generally unreactive toward the ground electronic state atomic carbon such as in ethane (C2H6). The statistical theory predicts the overall product branching ratios at the experimental collision energy as 50% for 1-butyn-4-yl, 33% for 1,3-butadien-2-yl, i-C4H5, and 11% for 1,3-butadien-1-yl, n-C4H5, with i-C4H5 (230 kJ mol-1 below the reactants) favored by the C-C insertion providing the best match with the experimentally observed reaction exoergicity. The C(3Pj) + c-C3H6 reaction is predicted to be a source of C4H5 radicals under the conditions where its low entrance barriers can be overcome, such as in planetary atmospheres or in circumstellar envelopes but not in cold molecular clouds. Both i- and n-C4H5 can further react with acetylene eventually producing the first aromatic ring and hence, the reaction of the atomic carbon with c-C3H6 can be considered as an initial step toward the formation of benzene.

Carbon Atom Insertion into Pyrroles and Indoles Promoted by Chlorodiazirines.

Herein, we report a reaction that selectively generates 3-arylpyridine and quinoline motifs by inserting aryl carbynyl cation equivalents into pyrrole and indole cores, respectively. By employing α-chlorodiazirines as thermal precursors to the corresponding chlorocarbenes, the traditional haloform-based protocol central to the parent Ciamician-Dennstedt rearrangement can be modified to directly afford 3-(hetero)arylpyridines and quinolines. Chlorodiazirines are conveniently prepared in a single step by oxidation of commercially available amidinium salts. Selectivity as a function of pyrrole substitution pattern was examined, and a predictive model based on steric effects is put forward, with DFT calculations supporting a selectivity-determining cyclopropanation step. Computations surprisingly indicate that the stereochemistry of cyclopropanation is of little consequence to the subsequent electrocyclic ring opening that forges the pyridine core, due to a compensatory homoaromatic stabilization that counterbalances orbital-controlled torquoselectivity effects. The utility of this skeletal transform is further demonstrated through the preparation of quinolinophanes and the skeletal editing of pharmaceutically relevant pyrroles.

A DFT study of methane conversion on Mo-terminated Mo2C carbides: Carburization vs C–C coupling

Molybdenum carbides have been believed to catalyze C–C coupling to generate aromatics from methane conversion. Herein, a systematic study of methane activation on the Mo-terminated Mo2C surfaces have been performed using density functional theory calculations. Our results indicate that the Mo-terminated β-Mo2C surface exhibits a superior activity toward methane activation. Carburization through insertion of carbon atoms into the subsurface interstitial sites of β-Mo2C reduces the reactivity towards methane activation; and complete carburization in the subsurface layer of β-Mo2C makes it behave similarly to α-Mo2C, which has a completely carburized subsurface layer, and α-MoC towards methane conversion. Consequently, dimerization of the CH* adspecies through CC coupling occurs more readily, resulting in C2H2*, a potential precursor to produce long chain hydrocarbons or aromatics. This study also demonstrates a dynamic nature of carburization of molybdenum carbides under the condition of methane activation, which is expected to play an important role in determining the activity and selectivity for, e.g., dehydro-aromatization.

Effect of Carbon Insertion on the Structural and Magnetic Properties of NdScSi.

The investigation of layered intermetallic compounds containing light elements like hydrogen has great potential for superconductivity. We studied the insertion of carbon atoms in CeScSi-type intermetallics (an ordered variant of the La2Sb structure type), and here, we report the new carbide NdScSiC0.5. Carbon insertion keeps the pristine compound's space group, I4/mmm, but causes an anisotropic expansion of the unit cell with an increase in the a parameter and a decrease of the c parameter. X-ray and neutron diffraction measurements indicate the existence of a NdScSiCx solid solution (0.2 < x ≤ 0.5) with carbon atoms occupying only the Sc4Nd2 octahedral sites while leaving the Nd4 tetrahedral sites vacant. Magnetization measurements unveil a linear reduction of the ferromagnetic ordering temperature from TC = ∼171 K to ∼50 K with increasing carbon content. The ferromagnetic structures of the pristine NdScSi and the filled NdScSiC0.5 have been determined from neutron diffraction measurements. Finally, we discuss the effect of carbon versus hydrogen insertion on electronic and magnetic properties based on density functional theory calculations. Although the unpaired spin density channels between Nd and Sc atoms (responsible of the high Curie temperature in NdScSi) are reduced upon carbon insertion, the strong Nd-C interaction, linked to a reduced c lattice parameter in NdScSiC0.5, ensures a strong magnetic coupling between the Nd double layer along the c axis and the ferromagnetic order is preserved.

Structural and magnetic investigation on tetragonal R-Fe alloy with 1:12 stoechiometry

Structure and magnetic proprieties of ball-milled Sm(Fe,Mo)12 compounds were carried out under an Ar atmosphere. Milled powders were subsequently annealed at a temperature ranging from 700°C up to 1200°C. The effects of heat treatment, on structure and magnetic property changes, have been investigated by means of x-ray diffraction using the Rietveld method, and differential sample magnetometer. At low temperature, Rietveld analysis has revealed the presence of new phase with the 1:10 stoechiometry. Insertion of carbon atoms was carried out via a solid - solid reaction either. Upon carbonation, the Curie temperature of samarium based alloy was enhanced. Besides, systematic analyses of the structural aspects have been undertaken upon insertion.

Simulation of carbon containing complexes at silicon–silicon grain boundaries in cluster approximation

The transformation of the “core” for the tilt Σ5 θ=37° [001]/(130) grain boundary (GB) in polycrystalline silicon due to incorporation of carbon atoms is studied with a method of molecular orbital–linear combinations of atomic orbital (MO LCAO) in PM3 approximation. Insertion of carbon atoms into 5- or 7-fold interstitial positions at GB “core” formed donor-like complexes which are composed of combined Si 2C, Si 3C or Si 4C configurations depending on number x of incorporated C-atoms. Energy levels of such complexes are shifted to the bottom of the conductive band from E C—0.536 eV to E C—0.043 eV with increasing x from 1 to 4.

Electronic structure of silicon carbide containing superstoichiometric carbon

Electronic structure of superstoichiometric silicon carbide, s-SiC x>1.0, was studied by the self-consistentab initio linearized “muffin-tin” orbital method. It is most likely that the formation of s-SiC x>1.0 occurs by replacement of silicon atoms by carbon atoms rather than by insertion of carbon atoms into interstitial lattice sites. The C→Si replacement is accompanied by lattice compression (the equilibrium lattice parameter for a superstoichiometric phase of composition Si0.75C1.25 is −2% smaller than for SiC). In the presence of superstoichiometric carbon the type of interaction between silicon and carbon atoms changes and additional bonds characteristic of diamond are formed.

ChemInform Abstract: Single Stereodifferentiation Associated with Carbon Atom Insertion During the Oxonium Ion‐Initiated Pinacol Rearrangement of Dihydrofuranyl and Dihydropyranyl Carbinols.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Single Stereodifferentiation Associated with Carbon Atom Insertion during the Oxonium Ion-Initiated Pinacol Rearrangement of Dihydrofuranyl and Dihydropyranyl Carbinols

The stereoselectivity of the acid-promoted rearrangement of dihydrofuranyl and dihydropyranyl carbinols to spirocyclic ketones has been examined. These kinetically controlled isomerizations result in the ring expansion of the hydroxyl-substituted ring with generation of a newly stereogenic spirocyclic carbon atom. All of the adducts formed from several 4,5-dihydrofurans and cyclobutanone, cyclopentanone, and 2,2-dimethylcyclopentanone proved to be reactive. Of the 5,6-dihydropyrans examined, only the cyclobutanone adducts were sufficiently reactive to warrant study. The product distributions arising from the furanoid systems were characterized by modest discrimination in most cases. The more stereodifferentiating pyranoid systems show product distributions as high as 30:1. These results are explained in terms of transition state geometries (conformationally more flexible in the five-membered examples) while also taking into account the principle of stereoelectronic control.

On the insertion of carbon atoms in B 12 icosahedra and the structural anisotropy of β-rhombohedral boron and boron carbide

X-Ray diffraction of β-rhombohedral boron doped with up to 1 at.% carbon and a model calculation of the anisotropic distortion of a single icosahedron were carried out. The carbon atoms substitute for boron, but only at polar sites of the B 12 icosahedra. Compared with a boron atom, the carbon atom is shifted by 0.115 Å (6.5%) towards the centre of the icosahedron. The application of the model calculation on boron carbide using structural data of other authors, partly confirmed by our own measurements, shows that the distortion of the unit cell of boron carbide parallel to c exceeds that of the icosahedron by far, while the distortions are similar for the a axis. These are double the corresponding distortion in β-rhombohedral boron. The effect of elementary cells of boron carbide without chains on the distortion of the structure is evident; the effect of an electron-phonon interaction seems possible. The anisotropy of the structural modifications is immediately correlated with the changes in the concentrations of structural elements.

Structural, Mössbauer and magnetic studies of DyFeC(B) permanent magnet alloys

A systematic characterization of the Dy 15 Fe 77( B 1− y C y ) 8 system with 0 ≤ y ≤ 1 by means of X-ray diffraction techniq ues, Mössbauer spectroscopy and thermomagnetic measurements has been performed. The existence of two magnetic carbides, Dy 2Fe 14C and Dy 2 Fe 17− x C y (3 ≤ x ≤ 0), was evidenced. Dy 2Fe 14C, formed only by relative long annealing at 9 00°C having a C doped Dy 2Fe 17 phase as precursor, has a tetragonal structure similar to that of the corresponding boride. The Curie temperature of Dy 2 Fe 14 B 1− y C y is lowered with C addition while a appreciable increase was observed when iron is partially substituted by cobalt in the Dy 15Fe 77C 8 system. The hyperfine parameters of the iron sites for the Mössbauer spectrum of the 2:14:1 tetragonal carbide are presented. Dy 2Fe 17- x C y is formed by annealing at T > 900°C. Variations of lattice parameters and magnetic properties suggest a variation in the phase stoichiometry. X-ray analysis indicate a disordered structure based on that of RE 2Fe 17 with insertion of carbon atoms on the plane of Dy layers. This phase, with reduced C insertion, is presented in the as-cast material.

YCoC and Isotypic Carbides with a New, Very Simple Structure Type

Abstract Crystal Structure, Equiatomic Ternary Rare Earth Metal Cobalt Carbides The crystal structure of the new compound YCoC was determined from X-ray powder data. It is tetragonal, space group P42/mmc, with a = 0.36500(4) nm, c = 0.68636(9) nm and Z = 2 formula units per cell. The residual for a refinement of Debye-Scherrer data is R = 0.048 for 22 structure factors and 3 variable parameters. The structure is of a new type with no variable positional parameter. The arrangement of the metal atoms corresponds to that of the CsCl structure. The tetragonal superstructure with a doubled c axis arises through the ordered insertion of carbon atoms on octahedral sites formed by four Y and two Co atoms. The hydrolysis of YCoC in hydrochloric acid yields mainly methane, propane, and ethane. The compounds LnCoC (Ln = Gd -Tm, Lu) are isotypic with YCoC.