Generation of NH-azomethine imine intermediates through the 1,2-hydrogen shift of hydrazones and their intermolecular cycloaddition reaction with olefinic dipolarophiles

The thermal 1,2-hydrogen shift of the hydrazone generates the NH-azomethine imine intermediate in the 4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carbaldehyde system under mild conditions. Therein, the resulting NH-azomethine imine should be stabilized by forming an internal hydrogen bond with the carbonyl oxygen at the 4-position. Its smooth stereoselective intermolecular cycloaddition reaction with olefinic dipolarophiles giving pyrazolidine derivatives is discussed.     

Synthesis of oxygen-containing heterocyclic compounds via α-chloro-δ-(trimethylsilyloxy)imines

Treatment of α-chloro-δ-(trimethylsilyloxy)ketimines, obtained by regiospecific alkylation of α-chloroketimines with 3-bromo-1-(trimethylsilyloxy)propane, with bases and nucleophiles leads to a variety of oxygen-containing heterocycles, including tetrahydrofurans and tetrahydropyrans.     

Development of [3]ferrocenophane-derived N/B frustrated Lewis pairs for the metal-free catalytic hydrogenation of imines

A series of novel [3]ferrocenophane-derived N/B frustrated Lewis pairs (FLPs) were synthesized and successfully applied to the catalytic hydrogenation of imines in 71–93% yields. This approach could be easily conducted on gram scale and provided versatile synthetic route for the key intermediate of sertraline hydrochloride without heavy metal residues.     

Asymmetric aza-Henry reaction of fluoromethylated imines catalyzed by cinchona-derived bifunctional thiourea

The asymmetric aza-Henry reaction of fluoromethyl imines derived from 4-methoxyaniline with nitromethane was achieved under mild conditions using cinchona-derived bifunctional thiourea as catalyst. A series of chiral fluoromethylated β-nitroamines were synthesized and their transformation to optically pure 4-fluoromethyl-2-imidazolidones was illustrated.     

Approaches to primary tert-alkyl amines as building blocks

Primary tert-alkyl amines include analogues of amantadine, a fragment commonly linked to pharmacophoric groups to enhance biological activity. The preparation of primary tert-alkyl amines is considered to be a difficult problem. Four synthetic procedures, some of which have been previously reported for the synthesis of amines with primary (RCH₂NH₂) or secondary (RR'CHNH₂) alkyl and/or aryl groups, were tested for the synthesis of primary tert-alkyl amines (RR′R″CNH₂) in aliphatic series including adamantane adducts. These procedures included the formation and reduction of tert-alkyl azides, the Ritter reaction in standard and modified conditions, the addition of organometallic reagents to N-tert-butyl sulfinyl ketimines and one-pot reactions between nitriles and organometallic reagents in the presence of a Lewis acid, Τi(iPrO)₄ or CeCl_3. These synthetic routes are unexplored for primary tert-alkyl amines. Studies on the synthetic routes for primary tert-alkyl amines are currently lacking. The reaction conditions and substrate limitations were studied for each procedure, with the first procedure being the most general and applicable also for compounds bearing bulky adducts.     

Reactions of Organic Azides with Half‐sandwich Complexes of Iridium: Preparation of Mono‐ and Bis(imine) Derivatives

Imine complexes [IrCl(η⁵‐C₅Me₅){κ¹‐NH=C(H)Ar}{P(OR)₃}]BPh₄ ( 1 , 2 ) (Ar = C₆H₅, 4‐CH₃C₆H₄; R = Me, Et) were prepared by allowing chloro complexes [IrCl₂(η⁵‐C₅Me₅){P(OR)₃}] to react with benzyl azides ArCH₂N₃. Bis(imine) complexes [Ir(η⁵‐C₅Me₅){κ¹‐NH=C(H)Ar}₂{P(OR)₃}](BPh₄)₂ ( 3 , 4 ) were also prepared by reacting [IrCl₂(η⁵‐C₅Me₅){P(OR)₃}] first with AgOTf and then with benzyl azide. Depending on the experimental conditions, treatment of the dinuclear complex [IrCl₂(η⁵‐C₅Me₅)]₂ with benzyl azide yielded mono‐ [IrCl₂(η⁵‐C₅Me₅){κ¹‐NH=C(H)Ar}] ( 5 ) and bis‐[IrCl(η⁵‐C₅Me₅){κ¹‐NH=C(H)Ar}₂]BPh₄ ( 6 ) imine derivatives. In contrast, treatment of chloro complexes [IrCl₂(η⁵‐C₅Me₅){P(OR)₃}] with phenyl azide C₆H₅N₃ gave amine derivatives [IrCl(η⁵‐C₅Me₅)(C₆H₅NH₂){P(OR)₃}]BPh₄ ( 7 , 8 ). The complexes were characterized spectroscopically (IR, NMR) and by X‐ray crystal structure determination of [IrCl(η⁵‐C₅Me₅){κ¹‐NH=C(H)C₆H₄‐4‐CH₃}{P(OEt)₃}]BPh₄ ( 2b ).     

"一锅法"N-(2-苯甲酰胺苯基)-水杨醛亚胺/TiCl4·2THF催化乙烯聚合

报道了4个含苯甲酰胺取代的水杨醛亚胺配体: N-(2-苯甲酰胺苯基)-水杨醛亚胺(L1)、 N-(2-苯甲酰胺苯基)-3-甲基水杨醛亚胺(L2)、 N-(2-苯甲酰胺苯基)-3-叔丁基水杨醛亚胺(L3)和N-(2-苯甲酰胺苯基)-3,5-二溴水杨醛亚胺(L4)的合成, 采用 ¹H NMR和HRMS对其结构进行了表征. 在助催化剂甲基铝氧烷(MAO)作用下, 以L3与TiCl₄·2THF为模型催化体系, 在最佳陈化条件(陈化温度为25 ℃, 陈化时间为30 min, 配体与TiCl₄·2THF的摩尔比3∶1)下, 考察了L1~L4/TiCl₄·2THF催化体系Al/Ti摩尔比、 反应时间、 反应温度和聚合压力, 以及配体结构等对乙烯聚合的影响. 结果表明, 随着在水杨醛骨架上氧原子邻位取代基位阻的增大, 催化体系的活性及所得聚乙烯的分子量均有增加, 其中以L3的催化活性最高, 达到224 kg PE/(mol Ti?h). 采用高温 ¹H NMR, ¹³C NMR, GPC-IR和DSC等对由不同配体L1~L4/TiCl₄·2THF得到的聚乙烯样品的微观结构与热性能进行了分析与表征, 结果显示样品为线性高密度聚乙烯, M_n=5.9×10 ⁴~11.9×10 ⁴, 分子量分布(PDI)为21.9~72.1.     

树枝状吡啶亚胺铬催化剂的合成及其催化性能研究

以1. 0代聚酰胺-胺树枝状大分子为配体骨架、吡啶二甲醛为原料,合成了一种新型树枝状吡啶亚胺(DPI)配体,再以CrCl_3·6H_2O为络合试剂,制备DPI-Cr催化剂。采用IR、UV-Vis、MS、元素分析等确证了产物结构。考察溶剂种类、助催化剂种类、反应温度、乙烯压力以及Al/Cr摩尔比对DPI-Cr催化乙烯齐聚性能的影响。结果表明,DPI-Cr催化剂表现出良好的催化活性和烯烃选择性,优化反应条件下,催化效率可达4. 91×10~4g/mol Cr·h,C_6和C_8选择性为73. 90%。     

Synthesis and characterization of epoxy resins containing imine group and their curing processes with aromatic diamine

The epoxy resins containing imine bonding were prepared from hydroxyl substituted Schiff base monomers in two steps. At the first step, hydroxyl substituted Schiff base monomers were synthesized via condensation reaction. At the second step, epoxy resins were synthesized from the reaction between Schiff base monomers and epichlorohydrine (EPC). Then curing processes of epoxy resins were achieved by p-phenylenediamine compound. The structures of resulting compounds were confirmed by FT-IR, UV-Vis and ¹H-NMR. TG-DTA and DSC measurements were performed for thermal characterizations of the compounds. Chemical resistances of the cured epoxy-amine systems were determined for coating applications in acidic, alkaline and organic solvents. HCl (10%, aqueous solution), NaOH (10%, aqueous solution), DMSO, DMF, N-methylpyrrolidone, ethanol, THF and acetone were used for corrosion tests. Chemical resistance data of the synthesized epoxy resins demonstrated that they have good chemical resistance against various acid, alkaline and common organic solvents. Surface morphologies of epoxy resin and the cured epoxy resin were determined with scanning electron microscopy (SEM) measurements. Also, optical band gap (E_g) values of Schiff base monomers and epoxy resins were calculated from UV-Vis measurements.     

Hydrogen-Bond Catalysis of Imine Exchange in Dynamic Covalent Systems

The reversibility of imine bonds has been exploited to great effect in the field of dynamic covalent chemistry, with applications such as preparation of functional systems, dynamic materials, molecular machines, and covalent organic frameworks. However, acid catalysis is commonly needed for efficient equilibration of imine mixtures. Herein, it is demonstrated that hydrogen bond donors such as thioureas and squaramides can catalyze the equilibration of dynamic imine systems under unprecedentedly mild conditions. Catalysis occurs in a range of solvents and in the presence of many sensitive additives, showing moderate to good rate accelerations for both imine metathesis and transimination with amines, hydrazines, and hydroxylamines. Furthermore, the catalyst proved simple to immobilize, introducing both reusability and extended control of the equilibration process.