Synthesis of 11‐cis‐Retinoids by Hydrosilylation–Protodesilylation of an 11,12‐Didehydro Precursor: Easy Access to 11‐ and 12‐Mono‐ and 11,12‐Dideuteroretinoids

An expeditious, highly efficient approach to 11‐cis‐retinoids was achieved by semihydrogenation of a readily available 11‐yne precursor through a hydrosilylation–protodesilylation protocol. The complete chemo‐, regio‐, and syn‐stereoselectivity of the method also allowed direct access to 11‐ and 12‐monodeutero‐, and 11,12‐dideutero‐11‐cis‐retinoids. The analogous trans series was not accessible by this route, and was synthesized by means of Hiyama coupling.     

Special Chiral C2‐Symmetric endo‐Biarylnorbornane: Synthesis and Structure Illustration

A highly efficient and practical synthesis for strained special scaffold of chiral endo‐biarylnorbornane starting from available norbornadione was achieved with direct stereoselective dehydroxylation of tertiary alcohol as the key step, and the structure was illustrated by X‐ray structural analysis.     

Electrophilic Bromination of N‐Acylated Cyclohex‐3‐en‐1‐amines: Synthesis of 7‐Azanorbornanes

The intramolecular bromo‐amidation and the dibromination‐cyclisation of the N‐acylcyclohex‐3‐en‐1‐amines 4, 8, 9, 11, 13, 14 , and 16 was studied in view of the synthesis of bicyclic amines that are of interest as building blocks and potential glycosidase inhibitors. The trifluoroacetamides 4, 9 , and 14 reacted with N‐bromosuccinimide (NBS) in AcOH to give dihydro‐1,3‐oxazines in good yields. The stereoselectivity of the dibromination of the alkenes 8 and 9 depends on the nature of the protecting group, the reagent, and the reaction conditions. Br₂ in CH₂Cl₂ transformed the alkenes 8 and 9 predominantly into diaxial trans,trans‐dibromides. Bromination of 9 with PhMe₃NBr₃ or with Br₂ in the presence of Et₄NBr gave predominantly the diequatorial trans,cis‐ 27 besides some trans,trans‐ 28 . A similar bromination of the C(5)‐substituted N‐acyl‐4‐aminocyclohexenes 11, 13, 14 , and 16 with PhMe₃NBr₃ was accompanied by intramolecular side reactions that were suppressed by the addition of excess Et₄NBr. Under these conditions, 11 gave diastereoselectively trans‐dibromides, while its reaction with Br₂ gave trans‐dibromides along with the dihydrooxazinone 31 . Also the carbamate 13 reacted with PhMe₃NBr₃/Et₄NBr selectively to the trans‐dibromide 32 and with Br₂ to the trans‐dibromides 32 and 33 , the dihydrooxazinone 34 , and the bicyclic ether 35 . Similarly, the trifluoroacetamide 14 provided the dibromide 36 (89%), while its reaction with Br₂ led to the dihydrooxazine 22 , and the dibromides 36 and 37 . The N‐benzyl‐N‐Boc derivative 16 did not yield any dibromide; it reacted with PhMe₃NBr₃/Et₄NBr to the dihydrooxazinone 38 , and with Br₂ to the oxazinone 38 and the bicyclic ether 39 . The high stereoselectivity of the bromination with PhMe₃NBr₃/Et₄NBr suggests an anchimeric assistance of the NHR substituent. Deprotection, cyclisation, and carbamoylation transformed the dibromides 27, 29 , and 32 into the 7‐azanorbornanes 42, 49 , and 53 . The diols 45 and 57 were obtained from 42 and 53 via HBr elimination and stereoselective dihydroxylation; they proved weak inhibitors of several glycosidases. In no case could the formation of a bicyclic azetidine (6‐azabicyclo[3.1.1]heptane) from the dibromides 26 and 30 be observed.     

Irreversible endo‐Selective Diels–Alder Reactions of Substituted Alkoxyfurans: A General Synthesis of endo‐Cantharimides

The [4+2] cycloaddition of 3‐alkoxyfurans with N‐substituted maleimides provides the first general route for preparing endo‐cantharimides. Unlike the corresponding reaction with 3H furans, the reaction can tolerate a broad range of 2‐substitued furans including alkyl, aromatic, and heteroaromatic groups. The cycloaddition products were converted into a range of cantharimide products with promising lead‐like properties for medicinal chemistry programs. Furthermore, the electron‐rich furans are shown to react with a variety of alternative dienophiles to generate 7‐oxabicyclo[2.2.1]heptane derivatives under mild conditions. DFT calculations have been performed to rationalize the activation effect of the 3‐alkoxy group on a furan Diels–Alder reaction.     

Dimorphic ErAgSn and TmAgSn – High‐Pressure and High‐Temperature Driven Phase Transitions

The stannides ErAgSn and TmAgSn have been investigated under high‐temperature (HT) and high‐pressure (HP) conditions in order to investigate their structural chemistry. ErAgSn and TmAgSn are dimorphic: normal‐pressure (NP) ErAgSn and HT‐TmAgSn crystallize into the NdPtSb type structure, P6₃mc, a = 466.3(1), c = 729.0(2) pm for NP‐ErAgSn and a = 465.4(1), c = 726.6(2) pm for HT‐TmAgSn. NP‐ErAgSn was obtained via arc‐melting of the elements and subsequent annealing at 970 K, while HT‐TmAgSn crystallized directly from the melt by rapidly quenching the arc‐melted sample. HT‐TmAgSn transforms to the ZrNiAl type low‐temperature modification upon annealing at 970 K. The high‐pressure (HP) modification of ErAgSn was synthesized under multianvil high‐pressure (11.5 GPa) high‐temperature (1420 K) conditions from NP‐ErAgSn: ZrNiAl type, , a = 728.7(2), c = 445.6(1) pm. The silver and tin atoms in NP‐ErAgSn and HT‐TmAgSn build up two‐dimensional, puckered [Ag₃Sn₃] networks (277 pm intralayer Ag–Sn distance in NP‐ErAgSn) that are charge‐balanced and separated by the erbium and thulium atoms. The fourth neighbor in the adjacent layer has a longer Ag–Sn distance of 298 pm. The [AgSn] network in HP‐ErAgSn is three‐dimensional. Each silver atom has four tin neighbors (281–285 pm Ag–Sn). The [AgSn] network leaves distorted hexagonal channels, which are filled with the erbium atoms. The crystal chemistry of the three phases is discussed.     

High‐Temperature Study of 2‐Methyl Furan and 2‐Methyl Tetrahydrofuran Combustion

The ignition behavior of methyl furan (2‐MF) and methyl tetrahydrofuran (2‐MTHF) is investigated using the shock tube technique. Experiments are carried out using homogeneous gaseous mixtures of fuel, oxygen, and argon with equivalence ratios, ?, of 0.5, 1.0, and 2.0 at average pressures of 3 and 12 atm over a temperature range of 1060–1300 K. In addition to ignition delay time measurements, fuel concentration time histories during ignition and pyrolysis of 2‐MTHF are obtained by means of laser absorption spectroscopy using a He–Ne laser at a fixed wavelength of 3.39 µm. With respect to ignition delay times, it is observed that under similar conditions of equivalence ratio and argon/oxygen ratio (D), 2‐MTHF has longer ignition delay times than 2‐MF at 3 atm. In addition, 2‐MTHF has longer ignition delay times than 2‐MF at higher temperatures for the case of 12 atm and under the same conditions of ? and D. The higher reactivity of 2‐MF, as indicated by shorter ignition delay times, is attributed to differences in chemical structure, whereby weaker C–H bond sites are more readily susceptible to radical attack than in 2‐MTHF. It is observed that ignition delay times of 2‐MTHF decrease with increasing equivalence ratio at 12 atm for fixed argon/oxygen ratio. Ignition delay times are compared with model predictions using recent chemical kinetic models of both fuels, showing that both models generally predict shorter ignition delay times than measured. The relatively higher absorption cross section of 2‐MTHF at 3.39 µm allows for its concentration time histories to be determined and compared to model predictions. In line with the observed discrepancy in ignition predictions, predicted 2‐MTHF concentration profiles are such that the fuel is shown to be more rapidly consumed than observed in the experiments. The study advances understanding of the combustion chemistry of these cyclic ethers that are potential alternative fuels.     

Heteroacene Synthesis through C−S Cross‐Coupling/5‐endo‐dig Cyclization

Highly efficient, one‐step synthesis of sulfur‐containing heteroacenes was achieved through palladium‐catalyzed C?S cross‐coupling of bis‐alkynes with thioacetate as hydrogen sulfide surrogate. Heteroacenes consisting of three, five, and seven fused aromatic rings were obtained in a single catalytic step by four‐, six‐, and eightfold C?S bond formation.     

Synthesis and Biological Activities of Novel 6‐Alkylamino‐11,12‐dihydro‐11‐arylbenzo[c]phenanthridine Derivatives

A series of novel benzo[c]phenanthridine derivatives 2a , 2b , 2c , 2d , 2e , 2f , 2g , 2h , 2i , 2j , 2k , 2l , 2m and 3a , 3b , 3c , 3d , 3e , 3f bearing an alkylamino side chain at their 6‐position were synthesized. All of the target compounds were confirmed by ¹H NMR, ¹³C NMR, and HRMS, and some of them were also characterized by IR and ¹⁹F NMR. The preliminary bioassays showed that the target compounds displayed fungicidal activities; for example, compound 2l showed 60.0% and 70.0% inhibitive activity against Alternaria solani and Cercospora arachidicola at 50 mg/L, respectively, and some compounds also displayed plant growth‐regulating activities.     

Cinnamoyl Derivatives of 7α‐Amino‐ and 7α‐(Aminomethyl)‐ N‐(cyclopropylmethyl)‐6,14‐endo‐ethanotetrahydronororipavines are High‐Potency Opioid Antagonists

Methods have been developed for the synthesis of 7α‐amino‐ and 7α‐(aminomethyl)‐N‐cyclopropylmethyl‐6,14‐endo‐ethanotetrahydronororipavines and their cinnamoyl derivatives (Schemes 1 and 3). In displacement binding assays, the cinnamoyl derivatives 4c and 5c had high affinity for opioid receptors, but no particular selectivity for any receptor type or differences in affinity between 4c and 5c (Table 1). In tissue assays for opioid receptor function, in which both 4c and 5c were potent antagonists, the aminomethyl derivative 5c was 20‐ to 70‐fold more potent than the amino derivative 4c (Table 2). These data are in keeping with previously reported in vivo data and confirm the major effect of the methylene spacer in 5c .     

High‐Temperature Electrochemistry: A Review

High‐temperature electrochemistry remains a relatively unexplored field of research, although in recent years significant developments have been made. This report details the main experimental methods and approaches to heating an electrochemical system under both isothermal and non‐isothermal conditions and gives an insight into the experimental and electroanalytical results obtainable under such conditions. It has been shown that the promotion of mass transport at high‐temperatures, through diffusion or convection, often results in increased current signals. This increase benefits electroanalytical measurements by lowering detection limits. High temperatures also usefully enhance the sensitivity of systems with sluggish kinetics.     

A Cascade Synthesis of Hetero‐arylated Triarylmethanes Through a Double 5‐endo‐dig Cyclization Sequence

A sequential two‐step method for the synthesis of hetero‐arylated triarylmethanes through a Ag‐catalyzed sequential double cyclization–nucleophilic addition cascade is described. This methodology basically involves an initial 5‐endo‐dig cyclization of o‐alkynyl anilines to provide 2‐substituted indole derivatives, which then react with 2‐(2‐enynyl)‐pyridines to afford indolizine‐containing unsymmetrical triarylmethanes through another 5‐endo‐dig cyclization.     

Cyano‐Bridged ‘Oximato’ Complexes: Synthesis,Structure, and Catalase‐Like Activities

The reaction of the ‘oximato’‐ligand precursor A (Fig. 1) and metal salts with KCN gave two mononuclear complexes [ML(CN)(H₂O)_n](ClO₄) ( 1 and 2 ; L={N‐(hydroxy‐κO)‐α‐oxo‐N′‐[(pyridin‐2‐yl‐κN)methyl[1,1′‐biphenyl]‐4‐ethanimidamidato‐κN′}; M=Co^II ( 1 ), Cu^II ( 2 ); n=2 for Co^II, n=0 for Cu^II; Figs. 2 and 3). The new cyano‐bridged pentanuclear ‘oximato’ complexes [{ML(H₂O)_n(NC)}₄M¹(H₂O)_x](ClO₄)₂ ( 3 – 6 ) and trinuclear complexes [{ML(H₂O)_n(NC)}₂M¹L](ClO₄) ( 7 – 10 ) ([M¹=Mn^II, Cu^II; x=2 for Mn^II, x=0 for Cu^II] were synthesized from mononuclear complexes and characterized by elemental analyses, magnetic susceptibility, molar conductance, and IR and thermal analysis. The four [ML(CN)(H₂O)_n]⁺ moieties are connected by a metal(II) ion in the pentanuclear complexe 3 – 6 , each one involving four cyano bridging ligands (Fig. 4). The central metal ion displays a square‐planar or octahedral geometry, with the cyano bridging ligands forming the equatorial plane. The axial positions are occupied by two aqua ligands in the case of the central Mn‐atom. The two [ML(CN)(H₂O)_n]⁺ moieties and an ‘oximato’ ligand are connected by a metal(II) ion in the trinuclear complexes 7 – 10 , each one involving two cyano bridging ligands (Fig. 5). The central metal ions display a distorted square‐pyramidal geometry, with two cyano bridging ligands and the donor atoms of the tridentate ‘oximato’ ligand. Moreover catalytic activities of the complexes for the disproportionation of hydrogen peroxide (H₂O₂) were also investigated in the presence of 1H‐imidazole. The synthesized homopolynuclear Cu^II complexes 6 and 10 displayed eficiency in disproportion reactions of H₂O₂ producing H₂O and dioxygen thus showing catalase‐like activity.     

Continuous Flow Organic Synthesis under High‐Temperature/Pressure Conditions

Microreactor technology and continuous flow processing in general are key features in making organic synthesis both more economical and environmentally friendly. When preformed under a high‐temperature/pressure process intensification regime many transformations originally not considered suitable for flow synthesis owing to long reaction times can be converted into high‐speed flow chemistry protocols that can operate at production‐scale quantities. This Focus Review summarizes the state of the art in high‐temperature/pressure microreactor technology and provides a survey of successful applications of this technique from the recent synthetic organic chemistry literature.     

Synthesis,Structure, and Characterization of 3, 4′‐Bis‐1H‐1, 2,4‐triazolium Picrate Salt: A New High‐Energy Density Material

The environmentally friendly high‐energy density salt (TRTR)(PA) (TRTR = 3, 4′‐bis‐1, 2,4‐1H‐triazole, PA = 2, 4,6‐trinitrophenol, picric acid) was synthesized and characterized. The X‐ray single crystal diffraction results illustrate that the structure of title salt belongs to the monoclinic system, space group P2₁/c. Many parallel relationships exist in the molecule, as well as a strong intramolecular π–π stacking interaction. The DSC result shows only one exothermal decomposition step at 229.1 °C. The TG‐DTG curve demonstrates a 75.9 % mass loss from 180 °C to 300 °C at a rate of 3.01 % · K^–1. Experimental data show that the combustion heat approximately equals to TNT (–15.22 MJ · kg^–1) and the enthalpy of formation is +332.2 kJ · mol^–1. Non–isothermal kinetic and thermodynamic parameters were obtained by two methods (Kissinger and Ozawa). Detonation pressure and velocity were calculated to be 23.4 GPa and 7.32 km · s^–1, respectively. Additionally, the sensitivities towards impact and friction were assessed with relevant standard methods.     

High‐Temperature Elastic Moduli of Flux‐Grown α‐GeO2 Single Crystal

From high‐precision Brillouin spectroscopy measurements, six elastic constants (C₁₁, C₃₃, C₄₄, C₆₆, C₁₂, and C₁₄) of a flux‐grown GeO₂ single crystal with the α‐quartz‐like structure are obtained in the 298–1273 K temperature range. High‐temperature powder X‐ray diffraction data is collected to determine the temperature dependence of the lattice parameters and the volume thermal expansion coefficients. The temperature dependence of the mass density, ρ, is evaluated and used to estimate the thermal dependence of its refractive indices (ordinary and extraordinary), according to the Lorentz–Lorenz equation. The extraction of the ambient piezoelectric stress contribution, e₁₁, from the C′₁₁–C₁₁ difference gives, for the piezoelectric strain coefficient d₁₁, a value of 5.7(2) pC N^?1, which is more than twice that of α‐quartz. As the quartz structure of α‐GeO₂ remains stable until melting, piezoelectric activity is observed until 1273 K.