简单的末端烯烃异构化为具有 Z 立体化学的内部异构体的情况很少见,因为通常会形成更稳定的 E 异构体。我们在这里表明,由庞大的 β-二酮亚胺配体支撑的钴 (II) 催化剂具有适当的动力学选择性来催化一些简单的 1-烯烃的异构化,特别是作为稳定性较差的 Z-异构体的 2-烯烃。催化通过“烷基”机制进行,三配位钴 (II) 烷基配合物作为静止状态。如同位素标记实验所示,β-氢化物消除和 [1,2]-插入步骤都很快。立体模型通过在 β-氢化物消除的过渡态钴 (II) 处的方形平面几何结构来解释选择性。该催化剂不仅适用于简单的烯烃,还适用于高烯丙基硅烷、缩酮、和甲硅烷基醚。从与不良底物的反应中分离出钴 (I) 或钴 (II) 产物表明,关键的催化剂分解途径是双分子的,降低催化剂浓度通常会提高选择性。除了潜在有用的选择性转化之外,这些研究还为高自旋钴配合物催化烯烃异构化提供了机理理解,并证明了空间体
In Situ Generated Bulky Palladium Hydride Complexes as Catalysts for the Efficient Isomerization of Olefins. Selective Transformation of Terminal Alkenes to 2-Alkenes
作者:Delphine Gauthier、Anders T. Lindhardt、Esben P. K. Olsen、Jacob Overgaard、Troels Skrydstrup
DOI:10.1021/ja9108424
日期:2010.6.16
enriched substrates provided products without epimerization at the allylic stereogenic carbon centers. Finally, some mechanisticinvestigations were undertaken to understand the nature of the active in situ generated Pd-H catalyst. These studies revealed that the catalytic system is highly dependent on the large steric demand of the P(tBu)(3) ligand. The use of an alternative ligand, cataCXium PinCy, also
Stereoselective expoxidation of allylic and homoallylic alcohols with 30% hydrogen peroxide catalyzed by tungstic acid in buffered media
作者:Denis Prat、Bernard Delpech、Robert Lett
DOI:10.1016/s0040-4039(00)84080-0
日期:1986.1
The aqueous tungstic acid-catalyzed hydrogenperoxideepoxidation of allylicalcohols affords the same major diastereoisomer as the VO(acac)2/tBuOOH system with quite comparable stereoselectivities. In contrast, epoxidation of homoallylic alcohols appears to be much less stereoselective.
highly regioselective, fluoride‐catalyzed hydrosilylation of β‐hydroxy epoxides has been developed. The reaction is modular and applicable to the synthesis of a broad range of 1,4‐diols. Fluoride is crucial for two reasons: First, it promotes the formation of a silyl ether (which contains a Si‐H bond) and, second, it enables ringopening by an intramolecular SN2 reaction through activation of the silane
已经开发出一种新型的高度区域选择性,氟化物催化的β-羟基环氧化物的氢化硅烷化方法。该反应是模块化的,适用于多种1,4-二醇的合成。氟化物至关重要是因为两个原因:首先,它促进了甲硅烷基醚(含有Si-H键)的形成;其次,它通过分子内的S N 2反应通过硅烷的活化而使开环成为可能。该反应可以在空气中进行。
An Alternative Mechanism for the Cobalt-Catalyzed Isomerization of Terminal Alkenes to (<i>Z</i>)-2-Alkenes
作者:Anastasia Schmidt、Alexander R. Nödling、Gerhard Hilt
DOI:10.1002/anie.201409902
日期:2015.1.12
The cobalt‐catalyzed selective isomerization of terminal alkenes to the thermodynamically less‐stable (Z)‐2‐alkenes at ambient temperatures takes place by a new mechanism involving the transfer of a hydrogen atom from a Ph2PH ligand to the starting material and the formation of a phosphenium complex, which recycles the Ph2PH complex through a 1,2‐H shift.
Stereocontrol in intramolecular hydrosilylation of allyl and homoallyl alcohols: a new approach to the stereoselective synthesis of 1,3-diol skeletons
作者:Kohei. Tamao、Takashi. Nakajima、Ritsuo. Sumiya、Hitoshi. Arai、Noriko. Higuchi、Yoshihiko. Ito
DOI:10.1021/ja00279a097
日期:1986.9
31.30; H, 5.22; N, 36.52. Found: C, 31.34; H, 5.25; N, 36.70. Low-resolution mass spectral analysis showed the expected molecular ion at m / e 345. The infrared spectrum contained a cyano stretching peak at 2180 cm-'. The 31P NMR spectrum consisted of a singlet at -7.8 ppm. Crystals suitable for X-ray analysis were grown by slow evaporation of a solution of 2 in hexane. The structure of 2 is illustrated