Superelectrophilic Diels–Alder reactions and oxidations leading to heterocyclic biaryl compounds

Heterocyclic imines provide biaryl products by a two-step transformation. The first transformation involves a Diels–Alder reaction with a multiply protonated imine to give a tetrahydroquinoline product, whereas the second step involves oxidation with elemental sulfur at 260?°C.     

Aerobic Dehydrogenation of N-Heterocycles with Grubbs Catalyst: Its Application to Assisted-Tandem Catalysis to Construct N-Containing Fused Heteroarenes

An aerobic dehydrogenation of nitrogen-containing heterocycles catalyzed by Grubbs catalyst is developed. The reaction is applicable to various nitrogen-containing heterocycles. The exceptionally high functional group compatibility of this method was confirmed by the oxidation of an unprotected dihydroindolactam V to indolactam V. Furthermore, by taking advantage of the oxygen-mediated structural change of the Grubbs catalyst, we integrated ring-closing metathesis and subsequent aerobic dehydrogenation to develop the novel assisted-tandem catalysis using molecular oxygen as a chemical trigger. The utility of the assisted-tandem catalysis was demonstrated by the concise synthesis of N-containing fused heteroarenes including a natural antibiotic, pyocyanine.     

Success or Failure of Chiral Crystallization of Similar Heterocyclic Compounds

Single crystals of two achiral and planar heterocyclic compounds, C₉H₈H₃O(CA1) and C₈H₅NO₂ (CA4), recrystallized from ethanol, were characterized by single crystal X-ray analysis, respectively, and chiral crystallization was observed only for CA1 as P2₁2₁2₁ (# 19), whereas it was not observed for CA4 P2₁/c (# 14). In CA1, as a monohydrate, the hydrogen bonds were pronounced around the water of crystallization (O4), and the planar cyclic sites were arranged in parallel to slightly tilted positions. On the other hand, an anhydride CA4 formed a dimer by hydrogen bonds between adjacent molecules in the crystal, which were aggregated by van der Waals forces and placed in parallel planar cyclic sites.     

Practical routes to diacetylenic ketones and their application for the preparation of alkynyl substituted pyridines, pyrimidines and pyrazoles

Alkynyl substituted pyridines, pyrimidines and pyrazoles have been synthesised by cyclocondensations of diacetylenic ketones with enamines, amidines and hydrazines, respectively.     

Synthesis and cascade rearrangement of 3-arylazo-4-(3-ethoxycarbonylureido)furoxans

3-Arylazo-4-(3-ethoxycarbonylureido)furoxans, which were synthesized by the reactions of 4-amino-3-arylazofuroxans with ethoxycarbonyl isocyanate, were subjected to cascade rearrangements under the action of potassium tert-butoxide in dimethylformamide or by heating in dimethyl sulfoxide to form 4-amino-2-aryl-5-nitro-2H-1,2,3-triazoles. X-ray diffraction study and quantum-chemical calculations (B3LYP/6-31G**) of one of ureidofuroxans demonstrated that the intramolecular contact between the carbonyl group and the nitrogen atom of furoxan corresponds to the charge transfer from the lone electron pair of the oxygen atom to the antibonding orbital of the N—O bond.     

Catalytic Conversion of CO2 to Cyclic Carbonates through Multifunctional Zinc‐Modified ZSM‐5 Zeolite

The production of fine chemicals using CO₂ as C₁ building block through inexpensive heterogeneous catalysts with high efficiency under low pressure is challenging. Herein we propose for the first time the utilization of a multifunctional heterogeneous zinc‐modified HZSM‐5 (ZnHZSM‐5) catalyst for upgrading CO₂ by incorporation into cyclic carbonates from CO₂ and epoxides. Owing to the nice surface properties such as abundant Lewis acid, Brønsted acid and Lewis base sites, large surface area, and plenty of micropores, CO₂ could be concentrated and well activated in ZnHZSM‐5 verified by CO₂‐TPD, TG‐MS, etc. Meanwhile, the epoxides were also activated through metal center and hydrogen bond. Therefore, the reaction can easily assemble at the catalyst interface and show exceptional performance, affording the aimed products with high yield of up to 99% in the presence of commercial tetra‐n‐propylammonium bromide (90% in kilogram scale with 0.004 mol% ZnHZSM‐5 and 0.015 mol% ⁿPr₄NBr).     

碳-氟键断裂用于构建氟代异噁唑化合物

含氟异噁唑骨架是许多药物及农药分子中的重要结构单元,其中单氟代异噁唑类化合物的合成方法还比较有限.从易得的α-三氟甲基-β-羰基酯出发,发展了基于碱促进的碳氟键断裂策略的氟代异噁唑化合物合成方法,该反应条件温和,操作简便,官能团兼容性良好,可以中等到较好的收率得到一系列3-氟代异噁唑化合物,且所得产物可进一步转化为生物活性分子的类似物.     

Pyrrole‐Modified Subporphyrins Bearing a Sulfur‐Containing Heterocyclic Unit

As new pyrrole‐modified subporphyrins (PMSubPs) bearing a sulfur‐containing heterocyclic unit, dithiazolosubporphyrin 5 , dithiazinosubchlorin 6 , and oxodithiazinosubchlorin 7 were synthesized from α‐fluorosubchlorophin 2 via α’‐selective nitration with Cu(NO₃)₂ followed by double S_N2 reaction with methyl 3‐mercaptopropionate as a key step. Oxidation of 5 with H₂O₂ in the presence of a tungsten catalyst afforded S,S‐dioxodithiazolosubporphyrin 8 and nitration of 5 with Cu(NO₃)₂·3H₂O gave β‐nitrodithiazolosubporphyrin 9 or β,β‐dinitrodithiazolosubporphyrins 10a and 10b depending on reaction conditions. In the solid‐states, the dithiazole units in 8 and 9 are almost planar but the dithiazine unit in 6 and the 2‐oxodithiazine unit in 7 are non‐planar. Compared to subchlorophin 1 , dithiazolosubporphyrin 5 possesses a significantly reduced diatropic ring current and a greatly perturbed absorption spectrum showing largely split Q‐like bands at 501 and 660 nm. These perturbed electronic and optical properties of 5 are considerably attenuated in 6 and 7 and completely vanished in 8 , suggesting the importance of disulfide bond for the large perturbation.     

含磷杂环化合物的重排反应、互补离子及取代基效应

本文应用电子轰击质谱(EIMS)及亚稳离子的测定技术,研究了十四种新合成的含磷杂环化合物的碎裂机理,着重探讨了此系列化合物的重排反应、互补离子及取代基效应对离子丰度的影响。     

含氮、磷四元不饱和杂环化合物的合成和表征

合成了含氮、磷四元不饱和化合物. 反应可能是通过phosphinidene对P—C＝N的1,3环加成反应过程进行的.