Efficient Intramolecular Hydroalkoxylation of Unactivated Alkenols Mediated by Recyclable Lanthanide Triflate Ionic Liquids: Scope and Mechanism
作者:Alma Dzudza、Tobin J. Marks
DOI:10.1002/chem.200902269
日期:2010.3.15
catalytic pathway that involves kinetically significant intramolecular proton transfer. The present activation parameters—enthalpy (ΔH≠)=18.2 (9) kcal mol−1, entropy (ΔS≠)=−17.0 (1.4) eu, and energy (Ea)=18.2 (8) kcal mol−1—suggest a highly organized transition state. Proton scavenging and coordinative probing results suggest that the lanthanide triflates are not simply precursors of free triflic acid. Based
[Ln(OTf)3 ]类型的镧系三氟甲磺酸盐配合物(Ln = La,Sm,Nd,Yb,Lu)可作为有效的可循环催化剂,用于伯/仲和脂族/芳族化合物的快速分子内加氢烷氧基化(HO)/环化咪唑基室温离子液体(RTIL)中的羟基烯烃,生成相应的呋喃,吡喃,螺双环呋喃,螺双环呋喃/吡喃,苯并呋喃和异色满衍生物。产物直接从催化溶液中分离出来,转化表现出马尔可夫尼科夫区域选择性,周转频率高达47 h -1在120°C下。初级烯醇环化的环大小速率依赖性为5> 6,与空间控制的过渡态一致。末端烯醇的加氢烷氧基化/环化速率比内部烯醇的加氢烷氧基化/环化速率稍快,这表明在环状过渡态中适度的空间需求。芳基官能化羟基烯烃的环化速率比线性烯醇的环化速率更快,而五元和五元/六元螺双环骨架也被区域选择性封闭。在主要的空间受限的烯醇的环化过程中,从La 3+(1.160Å)到Lu 3+,对金属离子半径的周转频率依赖性降低了约80倍(0
A New Generation of Alkoxyl Radical Precursors – Preparation and Properties ofN-(Alkoxy)-4-arylthiazole-2(3H)-thiones
efficient synthesis from p-substituted acetophenones. Alkylation of heterocycles 6–10 in the form of their potassium or tetraalkylammonium salts 11–15 affords N-alkoxy-4-arylthiazole-2(3H)-thiones 16–20 in good to satisfactory yields. The hitherto unknown thiones 16–20 have been subjected to a detailed structural investigation (NMR spectroscopy and X-ray crystallography) and furthermore to a mechanistic
Cobalt-catalyzed oxidative cyclization of gem -disubstituted conjugated alkenols
作者:Tânia M.F. Alves、Mateus O. Costa、Beatriz A.D. Bispo、Fabiana L. Pedrosa、Marco A.B. Ferreira
DOI:10.1016/j.tetlet.2016.06.064
日期:2016.7
Aryl gem-disubstituted conjugated alkenols underwent oxidativecyclization affording 2,5,5-trisubstituted tetrahydrofurans in reasonable yields and good diastereoselectivities using the reductive termination variation of the Mukaiyama aerobic oxidative reaction. Under oxidative termination, the same alkenols produced diols and ketonic by-products via the double hydration and beta-scission competing
Towards Improved Alkoxyl Radical Precursors - The Synthesis of <i>N</i>-Alkoxy-4-(<i>p</i>-chlorophenyl)thiazole-2(3<i>H</i>)-thiones
作者:Jens Hartung、Michaela Schwarz
DOI:10.1055/s-1997-5754
日期:1997.7
4-(p-Chlorophenyl)-3-hydroxythiazole-2(3H)-thione (3) can be prepared in good yields and in useful quantities from p-chloro acetophenone (1). 0-Alkylation of the cyclic thiohydroxamic acid 3 via the respective potassium or the tetraethyl ammonium salts affords the esters 4. A slightly modified procedure allows the conversion of the acid 3 to the mixed anhydrides 5. The esters 4 and the anhydrides 5 are colorless to yellowish crystalline compounds which show a good shelf life. Visible light photolysis of the N-alkoxy derivatives 4e-g and reactive hydrogen donors affords substituted tetrahydrofurans 7 or tetrahydropyrans 8 via an alkoxyl radical pathway.
triiodide was the most effective catalyst, whereas typical Lewis acids such as TiCl4, AlCl3, and BF3·OEt2 were ineffective. Many functional groups were successfully introduced, and these resulted in yields of 31–86%. Various styrene derivatives were also applicable to this reaction. Mechanistic investigation revealed that the present hydrofunctionalization proceeded through Brønsted acid-catalyzed intramolecular