Cycloaromatization of 1,4-pentadiynes: a viable possibility?

[structure: see text] The effects of several mostly sigma-withdrawing, pi-donating substituents X on the hitherto unknown Bergman-like cyclizations of 3-substituted 1,4-pentadiynes were studied at the BLYP/6-311+G//BLYP/6-31G level of theory. As the cyclization with X = OH(+) has the lowest barrier and is about thermoneutral, we predict that the title reaction is viable, for instance, through activation of derivatives with X = O with Lewis acids.     

Cascade C?N and C?O bond constructions for the synthesis of dibenzoimidazo[1,4]oxazepines catalyzed by CuI/o-phen

A novel method for the synthesis of dibenzo[b,f]imidazo[1,2-d][1,4]oxazepine derivatives was described via cascade Csp² N and Csp² O bond constructions. It was a crossed double Ullmann reactions using 4,5-diaryl-2-(2-hydroxylphenyl)-1H-imidazole as the double nucleophilic centers in the presence of Cs₂CO₃, while 1-bromo-2-iodobenzene was used as a substrate catalyzed by CuI and o-phenanthroline in good yields.     

Synthesis from d-mannose of 1,4-dideoxy-1,4-imino-l-ribitol and of the α-mannosidase inhibitor 1,4-dideoxy-1,4-imino-d-talitol

The syntheses of 1,4-dideoxy-l,4-imino-L-ribitol and of 1,4-dideoxy-l,4-imino-D-talitol from D-mannose are described. 1,4-Dideoxy-l,4-imino-D-talitol is a specific and competitive inhibitor of human liver α-mannosidase $\text{in vitro}$ and also blocks the lysosomal catabolism of asparigine-linked glycans of glycoproteins $\text{in vivo}$.     

Manganese‐Catalyzed Dehydrogenative [4+2] Annulation of N?H Imines and Alkynes by C?H/N?H Activation

Described herein is a manganese‐catalyzed dehydrogenative [4+2] annulation of N H imines and alkynes, a reaction providing highly atom‐economical access to diverse isoquinolines. This transformation represents the first example of manganese‐catalyzed C H activation of imines; the stoichiometric variant of the cyclomanganation was reported in 1971. The redox neutral reaction produces H₂ as the major byproduct and eliminates the need for any oxidants, external ligands, or additives, thus standing out from known isoquinoline synthesis by transition‐metal‐catalyzed C H activation. Mechanistic studies revealed the five‐membered manganacycle and manganese hydride species as key reaction intermediates in the catalytic cycle.     

Zur polarographischen Bestimmung von Maleins?ureanhydrid und von Naphthochinon-1,4 in Phthals?ureanhydrid

Ohne Zusammenfassung     

Thiophene-Fused 1,4-Diazapentalene: A Stable C=N-Containing π-Conjugated System with Restored Antiaromaticity

A thiophene-fused 1,4-diazapentalene (TAP) was rationally designed and synthesized as a C=N-containing 4n π-electron system that exhibits restored antiaromaticity impaired by the doping with C=N bonds. X-ray crystallographic analysis and quantum chemical calculations revealed that the annulation of thiophene rings with the 1,4-diazapentalene moiety resulted in a much higher antiaromaticity than the pristine 1,4-diazapentalene. These effects can be ascribed to the reduced bond alternation of the eight-membered-ring periphery caused by stabilization of the less-stable bond-shifted resonance structure upon increasing the degree of substitution of imine moieties. Consequently, TAP underwent facile hydrogenation even under mild conditions because of its pronounced antiaromaticity and the high aromaticity of the corresponding hydrogenated product H₂-TAP. In addition, the electrophilic C=N moieties in TAP led to the formation of a dense π-stacked structure. These results highlight the effect of partial replacement of C=C bonds with C=N bonds in antiaromatic π-electron systems.     

Quasi-Classical Trajectory Study on O++DH (v=0, j=0)→OD++H Reaction at Different Collision Energy

The quasi-classical trajectory calculations O⁺+DH (v=0, j=0)→OD⁺+H reactions on the RODRIGO potential energy surface have been carried out to study the isotope effect onstereo-dynamics at the collision energies of 1.0, 1.5, 2.0, and 2.5 eV. The distributions of dihedral angle P(φr) and the distributions of P(θr) are discussed. Furthermore, the angular distributions of the product rotational vectors in the form of polar plot in θr and φr are calculated. The differential cross section shows interesting phenomenon that the reaction is dominated by the direct reaction mechanism. Reaction probability and reaction cross section are also calculated. The calculations indicate that the stereo-dynamics properties of the title reactions are sensitive to the collision energy.     

准经典轨线研究Li+HF(v=0,j=O)→LiF+H反应动力学

基于Aguado等人拟合的APW势能面(PES),运用准经典轨线(QCT)方法,对反应Li+HF(v=0,j=0)→LiF+H的动力学性质进行了计算.主要研究了不同碰撞能条件下的反应截面、转动取向、产物散射角分布和竞争反应模式等.结果表明,该反应存在直接提取型和间接插入型两种反应模式,在低能量下反应以间接插入反应模式为主,能量大于200 meV时则以直接提取反应为主.     

A new ZnII two-dimensional coordination polymer, {[Zn(μ-4,4′-bipy)(1,4-ndc)(H2O)2] · (H2O)} n (4,4′-bipy= 4,4′-bipyridine and 1,4-ndc=1,4-naphthalenedicarboxylate)

A 2D Zn^II(μ-4,4′-bipy) coordination polymer with 1,4-naphthalenedicarboxylate, {[Zn(μ-4,4′-bipy)(1,4-ndc)(H₂O)₂] · (H₂O)} _n , has been synthesized, characterized and studied by X-ray crystallography. The structural studies show the Zn atoms have six-coordinate geometry with a distorted octahedral environment. The 2D structure is grown by hydrogen bonds into a hybrid three-dimensional network.     

Competitive Activation of C?H and C?X Bonds in Reactions of Pt+ with CH3X (X=F,Cl): Experiment and Theory

The reactions of Pt⁺ with CH₃X (X=F, Cl) are studied experimentally by employing an inductively coupled plasma/selected‐ion flow tube tandem mass spectrometer and theoretically by density functional theory. Dehydrogenation and HX elimination are found to be the primary reaction channels in the remarkably different ratios of 95:5 and 60:40 in the fast reactions of Pt⁺ with CH₃F and CH₃Cl, respectively. The observed kinetics are consistent with quantum chemistry calculations, which indicate that both channels in the reaction with CH₃F are exothermic with ground‐state Pt⁺(²D), but that HF elimination is prohibited kinetically because of a transition state that lies above the reactant entrance. The observed HF‐elimination channel is attributed to a slow reaction of CH₃F with excited‐state Pt⁺(⁴F) for which calculations predict a small barrier. The calculations also show that both the HCl‐elimination and dehydrogenation channels observed with CH₃Cl are thermodynamically and kinetically allowed, although the state‐specific product distributions could not be ascertained experimentally. Further CH₃F addition is observed with the primary products to produce PtCH₂⁺(CH₃F)_1,2 and PtCHF⁺(CH₃F)_1,2. With CH₃Cl, sequential HCl elimination is observed with PtCH₂⁺ to form PtC_nH_2n⁺ with n=2, 3, which then add CH₃Cl sequentially to form PtC₂H₄⁺(CH₃Cl)_1–3 and PtC₃H₆⁺(CH₃Cl)_1,2. Also, sequential addition is observed for PtCHCl⁺ to form PtCHCl⁺(CH₃Cl)_1,2.     

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.