催化不对称光诱导自由基反应

自由基反应的立体选择性调控一直是不对称催化领域的挑战性难题.近年来,光化学过程特别是可见光化学过程在有机合成中越来越受到研究人员的重视,光诱导自由基化学也再次进入人们的视野.相对传统的自由基化学,光诱导自由基化学反应条件温和,易于调控,为实现高效催化不对称自由基反应带来了新的契机,展示了蓬勃的发展潜力.本文根据光诱导产生自由基种类的不同,简要介绍最近该方向的研究进展.     

α''''-苯磺酰基-α,β-不饱和酮与环戊二烯的不对称催化Diels-Alder反应

在手性金属钛催化剂存在下，研究了α－苯磺酰基－α，β－不饱和酮与环戊二烯的不对称催化Ｄｉｅｌｓ－Ａｌｄｅｒ反应；讨论了亲双烯体上不同取代基对反应活性和环加成产物光学纯度的影响；鉴定了环加成产物的构型，得到了高收率和高光学纯度的环加成产物．     

氮-氧偶极化合物在不对称催化反应研究中的应用

氮-氧偶极化合物中的氮-氧偶极具有较强的极性, 表现出良好的亲电、亲核性能, 可与许多物质形成分子加成产物, 也可与许多金属离子和可提供空轨道的非金属原子形成配合物和发生配位作用. 近年来已发现, 手性和非手性的氮-氧偶极化合物可用于一些不对称催化反应中, 着重讨论这方面的进展状况.     

吡唑酮化合物在催化不对称反应中的应用

吡唑-5-酮类化合物在具有生物活性化合物中占有重要地位,该类化合物得到化学家们的广泛关注。吡唑-5-酮及其常见衍生物具有多个反应位点,可参与多种类型的不对称反应(如不对称加成反应、不对称环化反应和其他不对称反应类型)。本文主要从吡唑-5-酮类化合物参与的不对称催化反应类型进行分类,阐述了各类底物参与的反应类型及其主要反应位点,对近年来吡唑酮及其常见衍生物参与的不对称反应研究进展进行总结,并对其未来发展方向进行展望。     

钌1,2-萘醌-1-肟配合物对aldol C—C成键反应的催化作用

在钌1,2-萘醌-1-肟(1-nqo)配合物cis,cis-[Ru(1-nqo)₂(CO)(NCMe)] (1)或trans,trans-[Ru(1-nqo)₂(PBu₃)₂] (2)的作用下, 氰基乙酸乙酯与取代苯甲醛发生aldol C—C成键反应. 根据GC-MS检测及HPLC分离结果, 对二苯甲醛的二个醛基可分别或同时与氰基乙酸乙酯发生aldol反应. ¹H NMR表征结果证明, 二种产物的双键构型均为反式. 其它取代苯甲醛的反应均给出单一反式aldol产物, 这表明该催化反应具有立体选择性. 配合物1的催化活性稍差, 产率不超过60%, 而配合物2的催化活性要高于1, 最高产率达99%.     

催化不对称傅-克反应研究进展

催化不对称傅-克反应是构建具有光学活性芳基化合物最有效的方法之一。自从1877年报道了首例傅-克反应后,该反应得到化学家们的关注。最近二十年,许多手性双功能有机小分子催化剂（如金鸡纳碱、手性脯氨醇硅醚、手性磷酸、手性硫脲等）以及金属与手性配体（如手性双氮氧、手性双唑啉、手性席夫碱）形成的配合物催化剂被应用到各类不对称傅-克反应中。本文主要从反应的芳基底物类型分类,对近年来酚、吡咯、呋喃以及噻吩参与的不对称傅-克反应进行简要概述,同时对这类反应所存在的问题和局限性进行总结,并对今后发展方向作了展望。     

线型1,2-邻二萘醌-1-肟(1-nqo)钌配合物的合成

报道了含C_(16)长碳链线型1,2-邻二萘醌-1-肟(1-nqo)钌配合物trans-，cis- 及cis-，cis-[Ru(1-nqo)_2(CO)(spy)] (3)及(4)含C_(18)长碳链线型1-nqo钌配合 物cis-，cis-[Ru(1-nqo)_2(CO)(opy)] (5)，trans-，trans-[Ru(1-nqo)_2(opy) _2] (6)的合成。利用红外、FAB质谱、核磁共振氢谱及紫外-可见吸收光谱表征配 合物的结构，利用~1H-~1H偶合二维核磁技术对核磁共振峰进行指认。     

无溶剂条件下的不对称催化反应

本文综述了近年来在无溶剂条件下进行的一些不对称催化反应的进展, 着重介绍了无溶剂条件下的不对称Aldol反应、环氧化合物不对称开环反应、外消旋环氧化合物的拆分、不对称Diels-Alder反应、金属有机试剂对醛酮的不对称加成反应、不对称氢化反应、不对称氢甲酰化反应、不对称烯烃复分解反应、不对称Michael加成反应、不对称氧化反应、不对称Friedel-Crafts反应等, 同时展望了无溶剂不对称催化反应的研究前景。     

DNA-Based Asymmetric Inverse Electron-Demand Hetero-Diels–Alder

While artificial cyclases hold great promise in chemical synthesis, this work presents the first example of a DNA-catalyzed inverse electron-demand hetero-Diels–Alder (IEDHDA) between dihydrofuran and various α,β-unsaturated acyl imidazoles. The resulting fused bicyclic O,O-acetals containing three contiguous stereogenic centers are obtained in high yields (up to 99 %) and excellent diastereo- (up to >99:1 dr) and enantioselectivities (up to 95 % ee) using a low catalyst loading. Most importantly, these results show that the concept of DNA-based asymmetric catalysis can be expanded to new synthetic transformations offering an efficient, sustainable, and highly selective tool for the construction of chiral building blocks.     

An Enantioselective Approach to Heteroatom-Containing Bicyclic Derivatives via Inverse-Electron-Demand Diels−Alder Reactions

Chiral heteroatom-containing bicyclic scaffolds are important pharmacophores and prevalent in bioactive natural products and drug molecules. Herein, we report a unified approach for the divergent synthesis of chiral heteroatom-containing bicyclic derivatives by lanthanide (III)-catalyzed asymmetric inverse-electron-demand Diels–Alder reactions of 2-pyrones. These reactions occur with various readily available dihydropyrroles and dihydrofurans as dienophiles, providing a step-economical synthetic platform for densely functionalized cis-hydroindoles and cis-hydrobenzofurans with excellent yields and enantioselectivities. The synthetic utility of this approach is demonstrated by the concise synthesis of (–)-α-lycorane and (–)-lycorine alkaloids.     

Iodine-Catalyzed Aza-Diels–Alder Reactions of Aliphatic N-Arylaldimines

Iodine-catalyzed aza-Diels–Alder (Povarov) reaction of 3,4-dihydro-2H-pyran with in situ generated N-arylimines containing enolizable protons is described. This has given an easy way to introduce C-2 aliphatic substitution in tetrahydroquinolines.     

Utility of 2-Diphenylphosphoryloxy-1,3-Dienes in Multicomponent Hetero-Diels–Alder Reactions to Construct Functionalized Six-Membered Nitrogen Heterocycles

The utility of 2-diphenylphosphoryloxy-1,3-dienes for the construction of substituted six-membered nitrogen heterocycles is presented. These dienes undergo boron trifluoride-promoted aza-Diels–Alder reactions when reacted with imines or related species formed in situ using aldehydes and amine derivatives. The stability of the dienes allows this three-component reaction to be carried out with no special precautions to eliminate water or air. Thirty-one examples of this process are presented. The usefulness of the enol phosphate functional group is highlighted in further reactions after the cycloaddition step to generate functionalized piperidenes or pyridines.     

Enantiodivergent [4+2] Cycloaddition of Dienolates by Polyfunctional Lewis Acid/Zwitterion Catalysis

Diels–Alder reactions have become established as one of the most effective ways to prepare stereochemically complex six-membered rings. Different catalysis concepts have been reported, including dienophile activation by Lewis acids or H-bond donors and diene activation by bases. Herein we report a new concept, in which an acidic prodiene is acidified by a Lewis acid to facilitate deprotonation by an imidazolium–aryloxide entity within a polyfunctional catalyst. A metal dienolate is thus formed, while an imidazolium–ArOH moiety probably forms hydrogen bonds with the dienophile. The catalyst type, readily prepared in few steps in high overall yield, was applied to 3-hydroxy-2-pyrone and 3-hydroxy-2-pyridone as well as cyclopentenone prodienes. Maleimide, maleic anhydride, and nitroolefin dienophiles were employed. Kinetic, spectroscopic, and control experiments support a cooperative mode of action. High enantioselectivity was observed even with unprecedented TONs of up to 3680.     

Asymmetric Aza-Diels–Alder Reaction with Ion-Paired—Iron Lewis Acid—Brønsted Acid Catalyst

The development and use of a multiple-activation catalyst with ion-paired Lewis acid and Brønsted acid in an asymmetric aza-Diels–Alder reaction of simple dienes (non-Danishefsky-type electron-rich dienes) was achieved by utilizing the [FeBr₂]⁺[FeBr₄]⁻ combination prepared in situ from FeBr₃ and chiral phosphoric acid. Synergistic effects of the highly active ion-paired Lewis acid [FeBr₂]⁺[FeBr₄]⁻ and a chiral Brønsted acid are important for promoting the reaction with high turnover frequency and high enantioselectivity. The multiple-activation catalyst system was confirmed using synchrotron-based X-ray absorption fine structure measurements, and theoretical studies. This study reveals that the developed catalyst promoted the reaction not only by the interaction offered by the ion-paired Lewis acid and the Brønsted acid but also noncovalent interactions.