• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Chemistry: A European journal >Efficient Intramolecular Hydroalkoxylation of Unactivated Alkenols Mediated by Recyclable Lanthanide Triflate Ionic Liquids: Scope and Mechanism
【24h】

Efficient Intramolecular Hydroalkoxylation of Unactivated Alkenols Mediated by Recyclable Lanthanide Triflate Ionic Liquids: Scope and Mechanism

机译：可循环的镧系三氟甲磺酸离子液体介导的未活化的烯醇的有效分子内氢烷氧基化作用：范围和机理

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Lanthanide triflate complexes of the type [Ln(OTf)(3)] (Ln = La, Sm, Nd, Yb, Lu) serve as effective, recyclable catalysts for the rapid intramolecular hydroalkoxylation (HO)/cyclization of primary/secondary and aliphatic/aromatic hydroxyalkenes in imidazolium-based room-temperature ionic liquids (RTILs) to yield the corresponding furan, pyran, spirobicyclic furan, spirobicyclic furan/pyran, benzofuran, and isochroman derivatives. Products are straightforwardly isolated from the catalytic solution, conversions exhibit Markovnikov regioselectivity, and turnover frequencies are as high as 47 h(-1) at 120 degrees C. The ring-size rate dependence of the primary alkenol cyclizations is 5>6, consistent with a sterically controlled transition state. The hydroalkoxylation/cyclization rates of terminal alkenols are slightly more rapid than those of internal alkenols, which suggests modest steric demands in the cyclic transition state. Cyclization rates of aryl-functionalized hydroxyalkenes are more rapid than those of the linear alkenols, whereas five- and five/six-membered spirobicyclic skeletons are also regioselectively closed. In cyclization of primary, sterically encumbered alkenols, turnover-frequency dependence on metal-ionic radius decreases by approximately 80-fold on going from La3+ (1.160 angstrom) to Lu3+ (0.977 angstrom), presumably reflecting steric impediments along the reaction coordinate. The overall rate law for alkenol hydroalkoxylation/cyclization is nu approximate to k[catalyst](1)[alkenol](1). An observed ROH/ROD kinetic isotope effect of 2.48 (9) is suggestive of a catalytic pathway that involves kinetically significant intramolecular proton transfer. The present activation parameters-enthalpy (Delta H double dagger) = 18.2 (9) kcal mol(-1), entropy (Delta S double dagger) = 17.0 (1.4) eu, and energy (E-a) = 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 on the kinetic and mechanistic evidence, the proposed catalytic pathway invokes hydroxyl and olefin activation by the electron-deficient Ln(3+) center, and intramolecular H+ transfer, followed by alkoxide nucleophilic attack with ring closure.
机译：[Ln（OTf）（3）]型镧系三氟甲磺酸盐配合物（Ln = La，Sm，Nd，Yb，Lu）可作为有效的可回收催化剂，用于伯/仲和脂肪族分子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α-芳族羟基烯烃，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，并且在120摄氏度时转换频率高达47 h（-1）。主要烯醇环化的环尺寸速率依赖性为5> 6，与空间控制的过渡状态。末端链烯醇的加氢烷氧基化/环化速率比内部链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链烯醇的环化速率更快，而五元和五元/六元螺二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La3 +（1.160埃）到Lu3 +（0.977埃）时，对金属离子半径的周转频率依赖性降低了约80倍，大概是沿着反应坐标反映了空间障碍。烯醇加氢烷氧基化/环化的总速率定律近似为k [（1）] [烯醇]（1）。观察到的ROH / ROD动力学同位素效应为2.48（9），表明存在涉及动力学上显着的分子内质子转移的催化途径。当前激活参数-焓（ΔH双匕首）= 18.2（9）kcal mol（-1），熵（ΔS双匕首）= 17.0（1.4）eu和能量（Ea）= 18.2（8）kcal mol （-1）-建议高度组织化的过渡状态。质子清除和协调的探测结果表明，镧系元素三氟甲基磺酸不只是游离三氟甲磺酸的前体。基于动力学和机理的证据，拟议的催化途径通过缺电子的Ln（3+）中心和分子内H +转移来调用羟基和烯烃活化，然后进行醇盐亲核攻击并闭环。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号