Reactions of Secondary Amines with Dichlorocarbene Generated in Aqueous–Alkaline Medium in the Presence of N-Methylmorpholine N-Oxide

Russian Journal of Organic Chemistry - Dichlorocarbene generated from chloroform in aqueous–alkaline medium in the presence of N-methylmorpholine N-oxide is converted to phosgene which reacts...     

Carbon–Carbon Bond Formation by Radical Cyclization: Regioselective Synthesis of Spiro Heterocyclic Compounds by n Bu3SnH‐Mediated Reaction

Several spiro heterocyclic compounds have been regioselectively synthesized in excellent yield by ⁿ Bu₃SnH‐AIBN‐mediated radical cyclization of 4‐(2′‐bromoaryloxymethyl)‐1‐methylquinolin‐2(1H)‐ones in refluxing benzene under nitrogen for 4 h.     

Direct Mechanism of the First Carbon–Carbon Bond Formation in the Methanol-to-Hydrocarbons Process

In the past two decades, the reaction mechanism of C−C bond formation from either methanol or dimethyl ether (DME) in the methanol-to-hydrocarbons (MTH) process has been a highly controversial issue. Described here is the first observation of a surface methyleneoxy analogue, originating from the surface-activated DME, by in situ solid-state NMR spectroscopy, a species crucial to the first C−C bond formation in the MTH process. New insights into the first C−C bond formation were provided, thus suggesting DME/methanol activation and direct C−C bond formation by an interesting synergetic mechanism, involving C−H bond breakage and C−C bond coupling during the initial methanol reaction within the chemical environment of the zeolite catalyst.     

Unusual p‐Toluene Sulfonic Acid–Catalyzed Carbon–Carbon Bond Formation

Abstract

Attempts to synthesize the antidepressant drug atomoxetine directly by p-TSA‐catalyzed reaction between o‐cresol and N‐methyl‐3‐phenyl‐3‐hydroxypropyl amine in toluene at reflux temperature surprisingly resulted in the formation of ortho‐substituted phenol derivative. The structure is unambiguously confirmed by single crystal X-ray.     

Formation of γ-Lactones by the Reaction of π-Allylnickel Complexes with Carbon Dioxide

Recently, considerable interest has been shown in the reaction of carbon dioxide with olefins or alkynes caused by transition metal complexes. Incorporation of CO₂ in oligomerizations of butadiene¹⁾ and 1-hexyne²⁾ has been performed to give lactone derivatives by Pd-Ph₂ PCH₂ CH₂ PPh₂ and Ni (COD)₂-Ph₂P(CH₂)₄PPh₂ (COD : 1,5-cyclooctadiene) systems, respectively. Very recently, Jolly et al. reported the reaction of CO₂ with π-allylnickel complexes which are the key intermediates of the oligomerization of diolefins.³⁾ For example, bis (η-methylallyl) nickel reacts with CO₂ in the presence of a phosphine ligand to give a nickel carboxylate complex:     

Efficient Synthesis of Cyclic Sulfoximines from N-Propargylsulfinamides through Sulfur–Carbon Bond Formation

Cyclic sulfoximines were readily synthesized by the cyclization of N-propargylsulfinamides without using expensive and toxic metal catalysts. This cyclization proceeded without loss of optical purity of chiral sulfinamides through the unusual sulfur–carbon bond formation promoted by an inexpensive inorganic base. This stereospecific cyclization offers a general approach to the asymmetric synthesis of chiral cyclic sulfoximines as an emerging heterocycle in medicinal chemistry.     

Nitrogen–Carbon Bond Formation by Reactions of a Titanium–Potassium Dinitrogen Complex with Carbon Dioxide,tert-Butyl Isocyanate,and Phenylallene

Nitrogen–carbon bond-forming reactions at coordinated dinitrogen in a bifunctional titanium–potassium system are reported. A titanium atrane complex with a tris(aryloxide)methyl ligand ( 1 ) was treated with two equivalents of potassium naphthalenide under N₂ atmosphere to generate a bifunctional complex ( 2 ) in which N₂ binds end-on to two titanium centers and side-on to three potassium cations. Dinitrogen complex 2 reacted with carbon dioxide, tert-butyl isocyanate, and phenylallene, forming nitrogen–carbon bonds and affording diverse N-functionalized products. The reaction of 2 with CO₂ followed by addition of Me₃SiCl resulted in the formation of the starting complex 1 with concomitant release of silylated carboxyl hydrazines while the reaction with two equivalents of tert-butyl isocyanate proceeded by insertion into the Ti−N bonds. Treatment of 2 with phenylallene afforded vinyl-substituted hydrazido complexes.     

Efficient Covalent Bond Formation in Gas-Phase Peptide–Peptide Ion Complexes with the Photoleucine Stapler

Noncovalent complexes of hydrophobic peptides GLLLG and GLLLK with photoleucine (L*) tagged peptides G(L* _n L _m )K (n = 1,3, m = 2,0) were generated as singly charged ions in the gas phase and probed by photodissociation at 355 nm. Carbene intermediates produced by photodissociative loss of N₂ from the L* diazirine rings underwent insertion into X?H bonds of the target peptide moiety, forming covalent adducts with yields reaching 30%. Gas-phase sequencing of the covalent adducts revealed preferred bond formation at the C-terminal residue of the target peptide. Site-selective carbene insertion was achieved by placing the L* residue in different positions along the photopeptide chain, and the residues in the target peptide undergoing carbene insertion were identified by gas-phase ion sequencing that was aided by specific ¹³C labeling. Density functional theory calculations indicated that noncovalent binding to GL*L*L*K resulted in substantial changes of the (GLLLK + H)⁺ ground state conformation. The peptide moieties in [GL*L*LK + GLLLK + H]⁺ ion complexes were held together by hydrogen bonds, whereas dispersion interactions of the nonpolar groups were only secondary in ground-state 0 K structures. Born-Oppenheimer molecular dynamics for 100 ps trajectories of several different conformers at the 310 K laboratory temperature showed that noncovalent complexes developed multiple, residue-specific contacts between the diazirine carbons and GLLLK residues. The calculations pointed to the substantial fluidity of the nonpolar side chains in the complexes. Diazirine photochemistry in combination with Born-Oppenheimer molecular dynamics is a promising tool for investigations of peptide–peptide ion interactions in the gas phase.

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Initial Carbon−Carbon Bond Formation during the Early Stages of Methane Dehydroaromatization

Methane dehydroaromatization (MDA) is among the most challenging processes in catalysis science owing to the inherent harsh reaction conditions and fast catalyst deactivation. To improve this process, understanding the mechanism of the initial C−C bond formation is essential. However, consensus about the actual reaction mechanism is still to be achieved. In this work, using advanced magic-angle spinning (MAS) solid-state NMR spectroscopy, we study in detail the early stages of the reaction over a well-dispersed Mo/H-ZSM-5 catalyst. Simultaneous detection of acetylene (i.e., presumably the direct C−C bond-forming product from methane), methylidene, allenes, acetal, and surface-formate species, along with the typical olefinic/aromatic species, allow us to conclude the existence of at least two independent C−H activation pathways. Moreover, this study emphasizes the significance of mobility-dependent host–guest chemistry between an inorganic zeolite and its trapped organic species during heterogeneous catalysis.     

Silicon–Nitrogen Bond Formation via Heterodehydrocoupling and Catalytic N-Silylation

Silicon–nitrogen bond formation is an important subfield in main group chemistry, and catalysis is an attractive route for efficient, selective formation of these bonds. Indeed, heterodehydrocoupling and N-silylation offer facile methods for the synthesis of small molecules through the coupling of primary, secondary, and tertiary silanes with N-containing substrates such as amines, carbazoles, indoles, and pyrroles. However, the reactivity of these catalytic systems is far from uniform, and critical issues are often encountered with product selectivity, conversions, substrate scope, catalyst activation, and in some instances, competing side reactions. Herein, a catalogue of catalysts and their reactivity for Si−N heterodehydrocoupling and N-silylation are reported.     

Asymmetric Solid–Gas Hydrohalogenation of Unfunctionalized Olefins via Formation of Crystalline Cyclodextrin Complexes

Asymmetric solid–gas hydrohalogenation of styrene, -methylstyrene,allylbenzene, and 2-norbornene as unfunctionalized olefins was carried out by using theirchiral crystalline - and -cyclodextrin complexes by exposing them to gaseous HCl and HBrin the dark at room temperature. The optical purities of the Markovnikov products obtainedfrom the ionic addition of HCl to the included olefins appear considerably higher than thosefrom the reaction with HBr. The highest enantioselectivities of 58% and 62% enantiomericexcess (ee) were obtained for the hydrochlorination of 3-phenyl-1-propene (allylbenzene) inthe crystalline - and -cyclodextrin complexes, respectively, and both reactions, which hadlittle danger of racemization, gave (S)-(+)-2-chloro-1-phenylpropane as the same predominantproduct in moderate chemical yields. A much lower enantioselectivity (<10% ee) wasobserved in the hydrobromination of the same olefin in the solid - and -cyclodextrincomplexes involving a racemization reaction. The enantiofacial selection provided the (S)-enantiomer similarly during hydrochlorination.     

Intramolecular Metal-Free N−N Bond Formation with Heteroaromatic Amines: Mild Access to Fused-Triazapentalene Derivatives

Formation of N−N bonds may offer an original approach to various nitrogen-containing heterocycles with numerous applications. For this purpose, we found that readily available heteroaromatic amines are appropriate substrates for providing an efficient and innovative approach for the formation of N−N bonds in the presence of iodine (III) reagent in very mild conditions. This method makes it possible to synthesize nitrogen rich triazapentalene derivatives exhibiting fluorescent properties, inaccessible with existing approaches.     

Triple-Bond Directed Csp2−N Bond Formation with N-Fluorobenzenesulfonimide as Aminating Source: One-Step Transformation of Aldehydes into Amines

A metal-free, versatile triple-bond directed approach for the decarbonylative C−H amination of ortho-alkynyl quinoline/pyridine aldehydes using N-fluorobenzenesulfonimide as nitrogen source under mild reaction conditions has been described. The designed reaction strategy was triggered by trapping of fluorine by base with subsequent attack of bis(phenylsulfonyl)-λ²-azane on the carbonyl carbon of a heterocycle, which was gradually converted into the corresponding amine through a Curtius type rearrangement. This protocol provides a one-step approach for the conversion of aldehydes into amines in good yields. The synthesized amines were successfully transformed into biologically important pyrroloquinolines/pyridines.     

Spectroscopic Investigation of Chalcogen Bonding: Halide–Carbon Disulfide Complexes

A combined experimental and theoretical approach has been used to study intermolecular chalcogen bonding. Specifically, the chalcogen bonding occurring between halide anions and CS₂ molecules has been investigated using both anion photoelectron spectroscopy and high-level CCSD(T) calculations. The relative strength of the chalcogen bond has been determined computationally using the complex dissociation energies as well as experimentally using the electron stabilisation energies. The anion complexes featured dissociation energies on the order of 47 kJ/mol to 37 kJ/mol, decreasing with increasing halide size. Additionally, the corresponding neutral complexes have been examined computationally, and show three loosely-bound structural motifs and a molecular radical.     

pH-Controlled Reversible Folding of Copolymers via Formation of β-sheet Secondary Structures

Protein functions are enabled by their perfectly arranged 3D structure, which is the result of a hierarchical intramolecular folding process. Sequence-defined polypeptide chains form locally ordered secondary structures (i.e., α-helix and β-sheet) through hydrogen bonding between the backbone amides, shaping the overall tertiary structure. To generate similarly complex macromolecular architectures based on synthetic materials, a plethora of strategies have been developed to induce and control the folding of synthetic polymers. However, the degree of complexity of the structure-driving ensemble of interactions demonstrated by natural polymers is unreached, as synthesizing long sequence-defined polymers with functional backbones remains a challenge. Herein, we report the synthesis of hybrid peptide-N,N-Dimethylacrylamide copolymers via radical Ring-Opening Polymerization (rROP) of peptide containing macrocycles. The resulting synthetic polymers contain sequence-defined regions of β-sheet encoding amino acid sequences. Exploiting the pH responsiveness of the embedded sequences, protonation or deprotonation in water induces self-assembly of the peptide strands at an intramacromolecular level, driving polymer chain folding via formation of β-sheet secondary structures. We demonstrate that the folding behavior is sequence dependent and reversible.     

Plasma-Assisted Coupling Reactions of Dinitrogen and Carbon Dioxide Mediated by Monometallic YB1–4−⋅Anions: Carbon−Nitrogen Bond Formation

Transition-metal catalyzed coupling to form C−N bonds is significant in chemical science. However, the inert nature of N₂ and CO₂ renders their coupling quite challenging. Herein, we report the activation of dinitrogen in the mild plasma atmosphere by the gas-phase monometallic YB_1–4⁻ anions and further coupling of CO₂ to form C−N bonds by using mass spectrometry and theoretical calculation. The observed product anions are NCNBO⁻ and N(BO)₂⁻, accompanied by the formation of neutral products YO and YB_0–2NC, respectively. We can tune the reactivity and the type of products by manipulating the number of B atoms. The B atoms in YB_1–4N₂⁻ act as electron donors in CO₂ reduction reactions, and the carbon atom originating from CO₂ serves as an electron reservoir. This is the first example of gas-phase monometallic anions, which are capable to realize the functionalization of N₂ with CO₂ through C−N bond formation and N−N and C−O bond cleavage.     

Use of Iodosobenzene in Combination with Vilsmeier–Haack Reagent in Carbon–Carbon Bond Cleavage of Dehydroacetic Acid and Its Analogue

The reaction of dehydroacetic acid with iodosobenzene in combination with Vilsmeier–Haack reagent offers a new and convenient method for C‐C bond cleavage with the formation of 3‐chloro‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one.     

Hypervalent-Iodine-Mediated Carbon–Carbon Bond Cleavage and Dearomatization of 9H-Fluoren-9-ols

A transition-metal-free synthesis of spiro compounds from 9H-fluoren-9-ols mediated by hypervalent iodine is reported. In this reaction, an unprecedented β-carbon elimination of tertiary alkoxyliodine(III) to form new diaryliodonium salts is proposed. The obtained phenol intermediates undergo oxidative dearomatization to furnish a class of oxo-spiro compounds. This domino reaction significantly increases the complexity of these molecules and shows excellent regio- and stereoselectivity.     

Rhodium-Catalyzed Pauson–Khand-Type Cyclization of 1,5-Allene-Alkynes: A Chirality Transfer Strategy for Optically Active Bicyclic Ketones

An efficient chirality transfer in the [RhCl(CO)₂]₂-catalyzed [2+2+1] cyclization of optically active axially chiral 1,3-disubstituted allenynes with CO to access optically active bicyclopentenone compounds has been developed. The distal C=C bond of allenes reacted with the alknye unit and CO to afford [4.3.0]-bicyclic products with high ee values under mild reaction conditions with an excellent selectivity.